Theory and Simulations of Refractive Substructure in Resolved Scatter-Broadened Images

At radio wavelengths, scattering in the interstellar medium distorts the appearance of astronomical sources. Averaged over a scattering ensemble, the result is a blurred image of the source. However, Narayan & Goodman (1989) and Goodman & Narayan (1989) showed that for an incomplete average, scattering introduces refractive substructure in the image of a point source that is both persistent and wideband. We show that this substructure is quenched but not smoothed by an extended source. As a result, when the scatter-broadening is comparable to or exceeds the unscattered source size, the scattering can introduce spurious compact features into images. In addition, we derive efficient strategies to numerically compute realistic scattered images, and we present characteristic examples from simulations. Our results show that refractive substructure is an important consideration for ongoing missions at the highest angular resolutions, and we discuss specific implications for RadioAstron and the Event Horizon Telescope.Comment: Equation numbering in appendix now matches published version. Two minor typos correcte

Price and Profit: Investigating a Conundrum

Although few in number, studies consistently find that price explains little, if any, of the variation in profit across farms. This contrasts with farmers' opinions regarding the importance of price, as well as the use of price supports as a primary policy instrument. Using farm level data from the Illinois Farm Business Farm Management program for calendar years 1996 through 2004, a potential explanation for this conundrum is identified. Price is significantly more correlated with a farmer's variation in management return from year to year (approximately, +0.45) than with the variation in management return across farmers (approximately, +0.10). Thus, the conundrum arises out of different perspectives: farmers focus on the performance of their own farm over time while studies have focused on the variation among farms.Agricultural Finance,

Optimal Correlation Estimators for Quantized Signals

Using a maximum-likelihood criterion, we derive optimal correlation strategies for signals with and without digitization. We assume that the signals are drawn from zero-mean Gaussian distributions, as is expected in radio-astronomical applications, and we present correlation estimators both with and without a priori knowledge of the signal variances. We demonstrate that traditional estimators of correlation, which rely on averaging products, exhibit large and paradoxical noise when the correlation is strong. However, we also show that these estimators are fully optimal in the limit of vanishing correlation. We calculate the bias and noise in each of these estimators and discuss their suitability for implementation in modern digital correlators.Comment: 8 Pages, 3 Figures, Submitted to Ap

Average Crop Revenue Election, Crop Insurance, and Supplemental Revenue Assistance: Interactions and Overlap for Illinois and Kansas Farm Program Crops

Farm-level data from Illinois and Kansas for the 1991–2007 crops are used to examine the interaction and overlap among crop revenue insurance, Supplemental Revenue Assistance (SURE), and Average Crop Revenue Election (ACRE). Compared with 75% Crop Revenue Coverage Insurance (75% CRCP), ACRE provides more payments and has a greater impact on minimum farm revenue for the Illinois farms. In contrast, for the Kansas farms, 75% CRCP has the greater impact. SURE’s relative impact on the Illinois and Kansas farms depends on the metric. The overlap in payments from ACRE and 75% CRCP resulting from covering the same part of the revenue risk distribution is estimated to be less than 5% of ACRE payments. Several proposals for improving the farm safety net are discussed.Average Crop Revenue Election Program (ACRE), Crop Revenue Coverage Insurance (CRCP), farm policy, Food Conservation and Energy Act of 2008, Supplemental Revenue Assistance (SURE), Agribusiness, Agricultural and Food Policy, Farm Management, Land Economics/Use, Risk and Uncertainty, Q18, Q12,

UPDATING CORN PROGRAM PAYMENT YIELDS: ARE FARM OPERATORS DIFFERENTIALLY AFFECTED?

Crop yields which determine farm income deficiency payments have been frozen at 1981-1985 levels since 1986. Data from a longitudinal survey of Ohio farm operators are analyzed to evaluate whether updating payment yields will differentially affect farm operators. Results of the analysis imply that farm operators who operate larger farms, live in counties with higher yields, and have higher fertilizer and pesticide expenses per acre of corn will benefit more. In addition, low (high) existing payment yields are understated (overstated) relative to updated payment yields.Agricultural Finance,

POTENTIAL EFFECTS OF SUBSIDIZED LIVESTOCK INSURANCE ON LIVESTOCK PRODUCTION

Recent legislation has cleared the way for subsidized livestock price insurance. Such programs could increase production. Expected feeder cattle prices with and without subsidized insurance will be analyzed using E-V and Stochastic Dominance. Results will highlight the potential effects of the program on marketing risk and production decisions.Livestock Production/Industries, Risk and Uncertainty,

Primary pulmonary hypertension is associated with reduced pulmonary vascular expression of type II bone morphogenetic protein receptor

BACKGROUND: Mutations in the type II receptor for bone morphogenetic protein (BMPR-II), a receptor member of the transforming growth factor-beta (TGF-beta) superfamily, underlie many familial and sporadic cases of primary pulmonary hypertension (PPH). METHODS AND RESULTS: Because the sites of expression of BMPR-II in the normal and hypertensive lung are unknown, we studied the cellular localization of BMPR-II and the related type I and II receptors for TGF-beta by immunohistochemistry in lung sections from patients undergoing heart-lung transplantation for PPH (n=11, including 3 familial cases) or secondary pulmonary hypertension (n=6) and from unused donor lungs (n=4). In situ hybridization was performed for BMPR-II mRNA. Patients were screened for the presence of mutations in BMPR2. In normal lungs, BMPR-II expression was prominent on vascular endothelium, with minimal expression in airway and arterial smooth muscle. In pulmonary hypertension cases, the intensity of BMPR-II immunostaining varied between lesions but involved endothelial and myofibroblast components. Image analysis confirmed that expression of BMPR-II was markedly reduced in the peripheral lung of PPH patients, especially in those harboring heterozygous BMPR2 mutations. A less marked reduction was also observed in patients with secondary pulmonary hypertension. In contrast, there was no difference in level of staining for TGF-betaRII or the endothelial marker CD31. CONCLUSIONS: The cellular localization of BMPR-II is consistent with a role in the formation of pulmonary vascular lesions in PPH, and reduced BMPR-II expression may contribute to the process of vascular obliteration in severe pulmonary hypertension