The Impact of Reducing Greenhouse Gas Emissions in Crop Agriculture: A Spatial- and Production-Level Analysis

With the Waxman-Markey Bill passing the House and the administration’s push to reduce carbon emissions, the likelihood of the implementation of some form of a carbon emissions policy is increasing. This study estimates the greenhouse gas (GHG) emissions of the six largest row crops produced in Arkansas using 57 different production practices predominantly used and documented by the University of Arkansas Cooperative Extension Service. From these GHG emission estimates, a baseline state “carbon footprint†was estimated and a hypothetical GHG emissions reduction of 5, 10, and 20 percent was levied on Arkansas agriculture using a cap-and-trade method. Using current production technology and traditional land use choices, results show that the trading of carbon-emitting permits to reduce statewide GHG emissions by 5 percent from the baseline would enhance GHG emissions efficiency measured as net crop farm income generated per unit of carbon emissions created. The 5 percent reduction in GHG emissions does cause marginal reductions in acres farmed and has marginal income ramifications. Beyond the 5 percent reduction target, gains in GHG emissions efficiency decline but remain positive in most counties through the 10 percent GHG reduction target. However, with a 10 percent GHG reduction, acreage and income reductions more than double compared to the 5 percent level. When GHG emissions are reduced by 20 percent from the baseline, the result is a major cropping pattern shift coupled with significant reductions in traditional row crop acreage, income, and GHG emissions efficiency.greenhouse gas emissions, carbon equivalents, sustainability, cap and trade, Environmental Economics and Policy, Resource /Energy Economics and Policy,

Applications of vortex gas models to tornadogenesis and maintenance

Processes related to the production of vorticity in the forward and rear flank downdrafts and their interaction with the boundary layer are thought to play a role in tornadogenesis. We argue that an inverse energy cascade is a plausible mechanism for tornadogenesis and tornado maintenance and provide supporting evidence which is both numerical and observational. We apply a three-dimensional vortex gas model to supercritical vortices produced at the surface boundary layer possibly due to interactions of vortices brought to the surface by the rear flank downdraft and also to those related to the forward flank downdraft. Two-dimensional and three-dimensional vortex gas models are discussed, and the three-dimensional vortex gas model of Chorin, developed further by Flandoli and Gubinelli, is proposed as a model for intense small- scale subvortices found in tornadoes and in recent numerical studies by Orf et al. In this paper, the smaller scales are represented by intense, supercritical vortices, which transfer energy to the larger-scale tornadic flows (inverse energy cascade). We address the formation of these vortices as a result of the interaction of the flow with the surface and a boundary layer.Comment: 20 pages, 6 figure

Protein Structure Prediction: The Next Generation

Over the last 10-15 years a general understanding of the chemical reaction of protein folding has emerged from statistical mechanics. The lessons learned from protein folding kinetics based on energy landscape ideas have benefited protein structure prediction, in particular the development of coarse grained models. We survey results from blind structure prediction. We explore how second generation prediction energy functions can be developed by introducing information from an ensemble of previously simulated structures. This procedure relies on the assumption of a funnelled energy landscape keeping with the principle of minimal frustration. First generation simulated structures provide an improved input for associative memory energy functions in comparison to the experimental protein structures chosen on the basis of sequence alignment

Rods are less fragile than spheres: Structural relaxation in dense liquids composed of anisotropic particles

We perform extensive molecular dynamics simulations of dense liquids composed of bidisperse dimer- and ellipse-shaped particles in 2D that interact via repulsive contact forces. We measure the structural relaxation times obtained from the long-time decay of the self-part of the intermediate scattering function for the translational and rotational degrees of freedom (DOF) as a function of packing fraction \phi, temperature T, and aspect ratio \alpha. We are able to collapse the \phi and T-dependent structural relaxation times for disks, and dimers and ellipses over a wide range of \alpha, onto a universal scaling function {\cal F}_{\pm}(|\phi-\phi_0|,T,\alpha), which is similar to that employed in previous studies of dense liquids composed of purely repulsive spherical particles in 3D. {\cal F_{\pm}} for both the translational and rotational DOF are characterized by the \alpha-dependent scaling exponents \mu and \delta and packing fraction \phi_0(\alpha) that signals the crossover in the scaling form {\cal F}_{\pm} from hard-particle dynamics to super-Arrhenius behavior for each aspect ratio. We find that the fragility at \phi_0, m(\phi_0), decreases monotonically with increasing aspect ratio for both ellipses and dimers. Moreover, the results for the slow dynamics of dense liquids composed of dimer- and ellipse-shaped particles are qualitatively the same, despite the fact that zero-temperature static packings of dimers are isostatic, while static packings of ellipses are hypostatic.Comment: 10 pages, 17 figures, and 1 tabl

Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow

We perform molecular dynamics simulations of model granular systems undergoing boundary-driven planar shear flow in two spatial dimensions with the goal of developing a more complete understanding of how dense particulate systems respond to applied shear. In particular, we are interested in determining when these systems will possess linear velocity profiles and when they will develop highly localized velocity profiles in response to shear. In previous work on similar systems we showed that nonlinear velocity profiles form when the speed of the shearing boundary exceeds the speed of shear waves in the material. However, we find that nonlinear velocity profiles in these systems are unstable at very long times. The degree of nonlinearity slowly decreases in time; the velocity profiles become linear when the granular temperature and density profiles are uniform across the system at long times. We measure the time $t_l$ required for the velocity profiles to become linear and find that $t_l$ increases as a power-law with the speed of the shearing boundary and increases rapidly as the packing fraction approaches random close packing. We also performed simulations in which differences in the granular temperature across the system were maintained by vertically vibrating one of the boundaries during shear flow. We find that nonlinear velocity profiles form and are stable at long times if the difference in the granular temperature across the system exceeds a threshold value that is comparable to the glass transition temperature in an equilibrium system at the same average density. Finally, the sheared and vibrated systems form stable shear bands, or highly localized velocity profiles, when the applied shear stress is lowered below the yield stress of the static part of the system.Comment: 11 pages, 14 figure

Reversible plasticity in amorphous materials

A fundamental assumption in our understanding of material rheology is that when microscopic deformations are reversible, the material responds elastically to external loads. Plasticity, i.e. dissipative and irreversible macroscopic changes in a material, is assumed to be the consequence of irreversible microscopic events. Here we show direct evidence for reversible plastic events at the microscopic scale in both experiments and simulations of two-dimensional foam. In the simulations, we demonstrate a link between reversible plastic rearrangement events and pathways in the potential energy landscape of the system. These findings represent a fundamental change in our understanding of materials--microscopic reversibility does not necessarily imply elasticity.Comment: Revised pape

How A Cap-and-Trade Policy of Green House Gases Could Alter the Face of Agriculture in the South: A Spatial and Production Level Analysis.

With the Waxman-Markey Bill passing the House and the Obama administration’s push to reduce carbon emissions, the likelihood of the implementation of some form of a carbon policy is increasing. This study estimates the greenhouse gas (GHG) emissions of the six largest crops produced in Arkansas using 63 different production practices as documented by University of Arkansas Cooperative Extension Service. From these GHG estimates a baseline state “carbon footprint” was estimated and a hypothetical cap-and-trade carbon reduction of 5, 10, and 20% was levied on Arkansas agriculture. Results show that while a modest reduction in GHG emissions (5%) would only affect crop allocations amongst certain crops while marginally reducing state net returns, a 20% reduction would cause major cropping pattern shifts with some traditional row crops nearly disappearing.Cap-and-Trade, carbon, sustainability, Agricultural and Food Policy, Environmental Economics and Policy, Q28, Q52, Q54, Q56,

Differential effects of Alzheimer\u27s disease and Huntington\u27s disease on the performance of mental rotation

he ability to spatially rotate a mental image was compared in patients with Alzheimer\u27s disease (AD; n = 18) and patients with Huntington\u27s disease (HD; n = 18). Compared to their respective age-matched normal control (NC) group, the speed, but not the accuracy, of mental rotation abnormally decreased with increasing angle of orientation for patients with HD. In contrast, the accuracy, but not the speed, of rotation abnormally decreased with increasing angle of orientation for patients with AD. Additional analyses showed that these unique patterns of performance were not attributable to different speed/accuracy trade-off sensitivities. This double dissociation suggests that the distinct brain regions affected in the two diseases differentially contribute to speed and accuracy of mental rotation. Specifically, the slowing exhibited by HD patients may be mediated by damage to the basal ganglia, whereas the spatial manipulation deficit of AD patients may reflect pathology in parietal and temporal lobe association cortices important for visuospatial processing. (JINS, 2005, 11, 30–39.