Bioenergy Crop Production in the United States: Potential Quantities, Land Use Changes, and Economic Impacts on the Agricultural Sector

The U.S. Departments of Agriculture and Energyjointly analyzed the economic potential for,and impacts of, large-scale bioenergy cropproduction in the United States. Anagricultural sector model (POLYSYS) wasmodified to include three potential bioenergycrops (switchgrass, hybrid poplar, and willow). At farmgate prices of US $2.44/GJ, anestimated 17 million hectares of bioenergycrops, annually yielding 171 million dry Mg ofbiomass, could potentially be produced at aprofit greater than existing agricultural usesfor the land. The estimate assumes highproductivity management practices are permittedon Conservation Reserve Program lands. Traditional crops prices are estimated toincrease 9 to 14 percent above baseline pricesand farm income increases annually by US $6.0billion above baseline.At farmgate prices of US $1.83/GJ, anestimated 7.9 million hectares of bioenergycrops, annually yielding 55 million dry Mg ofbiomass, could potentially be produced at aprofit greater than existing agricultural usesfor the land. The estimate assumes managementpractices intended to achieve highenvironmental benefits on Conservation ReserveProgram lands. Traditional crops prices areestimated to increase 4 to 9 percent abovebaseline prices and farm income increasesannually by US $2.8 billion above baseline.     

Quasi-adiabatic shear zones in the lithosphere: numerical and experimental approaches

Continental breakup, or compressive lithosphere scale faulting, requires a physical mechanism for wholesale faulting of the lithosphere. We compared numerical and experimental models for the nucleation of quasi-adiabatic shear bands in polyvinylchloride (PVC) with those in an idealized viscoelastoplastic mantle with olivine rheology. In both materials fault nucleation is caused by elastic stress concentration on pre-existing imperfections, with localized yielding confined to its vicinity. Faulting occurs rapidly after the initial elastic energy in the system is charged sufficiently to cause wholesale yielding. Propagation of the fault, monitored by looking at the dissipation of plastic energy, reveals migration of a sharp, thermal-mechanical “crack”- like instability, which appears in the temperature field as a slightly diffused signal. The initial temperature rise in the crack is subtle but increases suddenly when the plate is severed. This autocatalytic behavior has also been described in ductile polymers, which can be used as mechanical analogues. We suggest that elastoplastic coupling in quasi-adiabatic shear banding is a key for fast (< 1 Ma) nucleation of shear zones. These nonlinear phenomena will be illustrated for both experimental and numerical results by nine movies     

A martingale characterization of equilibrium asset price processes

Summary. Bick (1987,1990) and He and Leland (1993) demonstrated that not every arbitrage-free Markovian diffusion price process is consistent with an equilibrium approach. We propose a unified framework for these results and we derive a new martingale characterization of equilibrium.     

Removing an ‘insuperable obstacle’ in the way of an objectivist analysis: Sraffa's attempts at fixed capital *

Abstract

The paper discusses Sraffa's consecutive attempts in the late 1920s and early 1940s to tackle a problem which endangered his objectivist, surplus-based approach to the theory of value and distribution aimed at reviving the standpoint of the classical economists. Whilst with circulating capital the value transfer to the product and the physical ‘destruction’ of the input are one and the same thing, with fixed capital this is not so. Sraffa eventually overcame the difficulty in terms of the joint products-method. This allowed him to explain relative prices and the rate of profits strictly in ‘material terms’.