Risk Analysis of Organic Cropping Systems in Minnesota

When all strategies received conventional market prices, 4-year cropping sequences had greater net returns than 2-year sequences, and the organic input, 4-year strategy had the highest net return. Adding 50% of the estimated organic premium, the 4-year, organic strategy dominated all low- and high-purchased input strategies.Crop Production/Industries, Risk and Uncertainty,

FAIR, POSTFAIR, AND NOFAIR: A COMPARISON OF CROPPING ALTERNATIVES FOR THE SOUTHERN GREAT PLAINS

The Federal Agriculture Improvement and Reform Act of 1996 was promoted as legislation that would enable and encourage farmers to base planting decisions on market incentives rather than commodity programs. Data from a designed experiment are used to compare the economics of three cropping systems for alternative commodity programs.Crop Production/Industries,

Density-density functionals and effective potentials in many-body electronic structure calculations

We demonstrate the existence of different density-density functionals designed to retain selected properties of the many-body ground state in a non-interacting solution starting from the standard density functional theory ground state. We focus on diffusion quantum Monte Carlo applications that require trial wave functions with optimal Fermion nodes. The theory is extensible and can be used to understand current practices in several electronic structure methods within a generalized density functional framework. The theory justifies and stimulates the search of optimal empirical density functionals and effective potentials for accurate calculations of the properties of real materials, but also cautions on the limits of their applicability. The concepts are tested and validated with a near-analytic model.Comment: five figure

Mantle heterogeneity during the formation of the North Atlantic Igneous Province: Constraints from trace element and Sr-Nd-Os-O isotope systematics of Baffin Island picrites

Sr-Nd-Os-O isotope and major and trace element data from ~62 Ma picrites from Baffin Island constrain the composition of mantle sources sampled at the inception of North Atlantic Igneous Province (NAIP) magmatism. We recognize two compositional types. Depleted (N-type) lavas have low 87Sr/86Sri (0.702990–0.703060) and 187Os/188Osi (0.1220–0.1247) and high 143Nd/144Ndi (0.512989–0.512999) and are depleted in incompatible elements relative to primitive mantle. Enriched (E-type) lavas have higher 87Sr/86Sri (0.703306–0.703851) and 187Os/188Osi (0.1261–0.1303), lower 143Nd/144Ndi (0.512825–0.512906), and incompatible element concentrations similar to, or more enriched than, primitive mantle. There is also a subtle difference in oxygen isotope composition; E-type lavas are marginally lower in δ18Oolivine value (5.16–4.84‰) than N-type lavas (5.15–5.22‰). Chemical and isotopic variations between E- and N-type lavas are inconsistent with assimilation of crust and/or subcontinental lithospheric mantle and appear to instead reflect mixing between melts derived from two distinct mantle sources. Strontium-Nd-O isotope compositions and incompatible trace element abundances of N-type lavas suggest these are largely derived from the depleted upper mantle. The 187Os/188Osi ratios of N-type lavas can also be explained by such a model but require that the depleted upper mantle had γOs of approximately −5 to −7 at 62 Ma. This range overlaps the lowest γOs values measured in abyssal peridotites. Baffin Island lava compositions are also permissive of a model involving recharging of depleted upper mantle with 3He-rich material from the lower mantle (Stuart et al., Nature, 424, 57–59, 2003), with the proviso that recharge had no recognizable effect on the lithophile trace element and Sr-Nd-Os-O isotope composition. The origin of the enriched mantle component sampled by Baffin Island lavas is less clear but may be metasomatized and high-temperature-altered recycled oceanic lithosphere transported within the proto Iceland plume. Differences between Baffin Island lavas and modern Icelandic basalts suggest that a range of enriched and depleted mantle sources have been tapped since the inception of magmatism in the province. Similarities between Baffin Island lavas erupted and those of similar age from East and West Greenland also suggest that the enriched component in Baffin Island lavas may have been sampled by lavas erupted over a wide geographic range

Efficient calculation of the antiferromagnetic phase diagram of the 3D Hubbard model

The Dynamical Cluster Approximation with Betts clusters is used to calculate the antiferromagnetic phase diagram of the 3D Hubbard model at half filling. Betts clusters are a set of periodic clusters which best reflect the properties of the lattice in the thermodynamic limit and provide an optimal finite-size scaling as a function of cluster size. Using a systematic finite-size scaling as a function of cluster space-time dimensions, we calculate the antiferromagnetic phase diagram. Our results are qualitatively consistent with the results of Staudt et al. [Eur. Phys. J. B 17 411 (2000)], but require the use of much smaller clusters: 48 compared to 1000

A Search for Distant Galactic Cepheids Toward l=60

We present results of a survey of a 6-square-degree region near l=60, b=0 to search for distant Milky Way Cepheids. Few MW Cepheids are known at distances >~ R_0, limiting large-scale MW disk models derived from Cepheid kinematics; this work was designed to find a sample of distant Cepheids for use in such models. The survey was conducted in the V and I bands over 8 epochs, to a limiting I~=18, with a total of ~ 5 million photometric observations of ~ 1 million stars. We present a catalog of 578 high-amplitude variables discovered in this field. Cepheid candidates were selected from this catalog on the basis of variability and color change, and observed again the following season. We confirm 10 of these candidates as Cepheids with periods from 4 to 8 days, most at distances > 3 kpc. Many of the Cepheids are heavily reddened by intervening dust, some with implied extinction A_V > 10 mag. With a future addition of infrared photometry and radial velocities, these stars alone can provide a constraint on R_0 to 8%, and in conjunction with other known Cepheids should provide good estimates of the global disk potential ellipticity.Comment: 18 pages, 4 tables, 13 figures (LaTeX / AASTeX

Current Induced Excitations in Cu/Co/Cu Single Ferromagnetic Layer Nanopillars

Current-induced magnetic excitations in Cu/Co/Cu single layer nanopillars (~50 nm in diameter) have been studied experimentally as a function of Co layer thickness at low temperatures for large applied fields perpendicular to the layers. For asymmetric junctions current induced excitations are observed at high current densities for only one polarity of the current and are absent at the same current densities in symmetric junctions. These observations confirm recent predictions of spin-transfer torque induced spin wave excitations in single layer junctions with a strong asymmetry in the spin accumulation in the leads.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Epitaxial Ferromagnetic Nanoislands of Cubic GdN in Hexagonal GaN

Periodic structures of GdN particles encapsulated in a single crystalline GaN matrix were prepared by plasma assisted molecular beam epitaxy. High resolution X-ray diffractometery shows that GdN islands, with rock salt structure are epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron microscopy combined with in-situ reflection high energy electron diffraction allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one due to GdN particles with Curie temperature of 70K and a second, anomalous room temperature phase.Comment: 4 pages, 3 figure

Pseudogap and antiferromagnetic correlations in the Hubbard model

Using the dynamical cluster approximation and quantum monte carlo we calculate the single-particle spectra of the Hubbard model with next-nearest neighbor hopping $t'$. In the underdoped region, we find that the pseudogap along the zone diagonal in the electron doped systems is due to long range antiferromagnetic correlations. The physics in the proximity of $(0,\pi)$ is dramatically influenced by $t'$ and determined by the short range correlations. The effect of $t'$ on the low energy ARPES spectra is weak except close to the zone edge. The short range correlations are sufficient to yield a pseudogap signal in the magnetic susceptibility, produce a concomitant gap in the single-particle spectra near $(\pi,\pi/2)$ but not necessarily at a location in the proximity of Fermi surface.Comment: 5 pages, 4 figure