Assessing the Costs and Environmental Consequences of Agricultural Land Use Changes: A Site-Specific, Policy-Scale Modeling Approach

The growth in federal conservation programs has created a need for policy modeling frameworks capable of measuring micro-level behavioral responses and macro-level landscape changes. This paper presents an empirical model that predicts crop choices, crop rotations, and conservation tillage adoption as a function of conservation payment levels, profits, and other variables at more than 42,000 agricultural sites of the National Resource Inventory (NRI) in the Upper Mississippi River Basin. Predicted changes in crop choices and tillage practices are then fed into site-specific environmental production functions to determine changes in nitrate runoff and leaching and in water and wind erosion at each NRI site. This policy-scale model is applied to the case of green payments for the adoption of conservation practices (conservation tillage and crop rotations) in the Upper Mississippi River Basin, a region under scrutiny as a significant source of nutrient loadings to the Mississippi River, causing hypoxia in the Gulf of Mexico. Results from this application suggest that payments for conservation tillage and crop rotations increase the use of these conservation practices. However, the acreage response is inelastic and the programs are not likely to be cost effective on their own for addressing the hypoxia problem in the Gulf of Mexico.agricultural policy, conservation practices, green payments, land use changes, nitrate runoff and leaching, non-point pollution, soil erosion.

Designs for the ATDRSS tri-band reflector antenna

Two approaches to design a tri-band reflector antenna for the Advanced TDRSS are examined. Two reflector antenna configurations utilizing frequency selective surfaces for operation in three frequency bands, S, Ku, and Ka, are proposed. Far-field patterns and the antenna feed losses were computed for each configuration. An offset-fed single reflector antenna configuration was adapted for conceptual spacecraft design. CADAM drawings were completed and a 1/13th scale model of the spacecraft was constructed

Friction and wear of plasma-deposited diamond films

Reciprocating sliding friction experiments in humid air and in dry nitrogen and unidirectional sliding friction experiments in ultrahigh vacuum were conducted with a natural diamond pin in contact with microwave-plasma-deposited diamond films. Diamond films with a surface roughness (R rms) ranging from 15 to 160 nm were produced by microwave-plasma-assisted chemical vapor deposition. In humid air and in dry nitrogen, abrasion occurred when the diamond pin made grooves in the surfaces of diamond films, and thus the initial coefficients of friction increased with increasing initial surface roughness. The equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. In vacuum the friction for diamond films contacting a diamond pin arose primarily from adhesion between the sliding surfaces. In these cases, the initial and equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. The equilibrium coefficients of friction were 0.02 to 0.04 in humid air and in dry nitrogen, but 1.5 to 1.8 in vacuum. The wear factor of the diamond films depended on the initial surface roughness, regardless of environment; it increased with increasing initial surface roughness. The wear factors were considerably higher in vacuum than in humid air and in dry nitrogen

Enhanced heat capacity and a new temperature instability in superfluid He-4 in the presence of a constant heat flux near T-lambda

We present the first experimental evidence that the heat capacity of superfluid 4He, at temperatures very close to the lambda point Tλ, is enhanced by a constant heat flux Q. The heat capacity at constant Q, CQ, is predicted to diverge at a temperature Tc(Q)<Tλ at which superflow becomes unstable. In agreement with previous measurements, we find that dissipation enters our cell at a temperature, TDAS(Q), below the theoretical value, Tc(Q). We argue that TDAS(Q) can be accounted for by a temperature instability at the cell wall, and is therefore distinct from Tc(Q). The excess heat capacity we measure has the predicted scaling behavior as a function of T and Q, but it is much larger than predicted by current theory

Automated Tetrahedral Mesh Generation for CFD Analysis of Aircraft in Conceptual Design

The paper introduces an automation process of generating a tetrahedral mesh for computational fluid dynamics (CFD) analysis of aircraft configurations in early conceptual design. The method was developed for CFD-based sonic boom analysis of supersonic configurations, but can be applied to aerodynamic analysis of aircraft configurations in any flight regime

Optimal definition of biological tumor volume using positron emission tomography in an animal model

BACKGROUND: The goal of the study is to investigate (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG-PET)’s ability to delineate the viable portion of a tumor in an animal model using cross-sectional histology as the validation standard. METHODS: Syngeneic mammary tumors were grown in female Lewis rats. Macroscopic histological images of the transverse tumor sections were paired with their corresponding FDG micro-PET slices of the same cranial-caudal location to form 51 pairs of co-registered images. A binary classification system based on four FDG-PET tumor contouring methods was applied to each pair of images: threshold based on (1) percentage of maximum tumor voxel counts (C(max)), (2) percentage of tumor peak voxel counts (C(peak)), (3) multiples of liver mean voxel counts (C(liver)) derived from PERCIST, and (4) an edge-detection-based automated contouring system. The sensitivity, which represented the percentage of viable tumor areas correctly delineated by the gross tumor area (GTA) generated from a particular tumor contouring method, and the ratio (expressed in percentage) of the overestimated areas of a gross tumor area (GTA(OE))/whole tumor areas on the macroscopic histology (WTA(H)), which represented how much a particular GTA extended into the normal structures surrounding the primary tumor target, were calculated. RESULTS: The receiver operating characteristic curves of all pairs of FDG-PET images have a mean area under the curve value of 0.934 (CI of 0.911–0.954), for representing how well each contouring method accurately delineated the viable tumor area. FDG-PET single value threshold tumor contouring based on 30 and 35 % of tumor C(max) or C(peak) and 6 × C(liver) + 2 × SD achieved a sensitivity greater than 90 % with a GTA(OE)/WTA(H) ratio less than 10 %. Contouring based on 50 % of C(max) or C(peak) had a much lower sensitivity of 67.2–75.6 % with a GTA(OE)/WTA(H) ratio of 1.1–1.7 %. Automated edge detection was not reliable in this system. CONCLUSIONS: Single-value-threshold tumor contouring using (18)F-FDG-PET is able to accurately delineate the viable portion of a tumor. 30 and 35 % of C(max), 30 and 35 % of C(peak), and 6 × C(liver) + 2 × SD are three appropriate threshold values to delineate viable tumor volume in our animal model. The commonly used threshold value of 50 % of C(max) or C(peak) failed to detect one third of the viable tumor volume in our model