Hexagonal Rare-Earth Manganites as Promising Photovoltaics and Light Polarizers

Ferroelectric materials possess a spontaneous electric polarization and may be utilized in various technological applications ranging from non-volatile memories to solar cells and light polarizers. Recently, hexagonal rare-earth manganites, h-RMnO$_3$ (R is a rare-earth ion) have attracted considerable interest due to their intricate multiferroic properties and improper ferroelectricity characterized by a sizable remnant polarization and high Curie temperature. Here, we demonstrate that these compounds can serve as very efficient photovoltaic materials and, in addition, possess remarkable optical anisotropy properties. Using first-principles methods based on density-functional theory and considering h-TbMnO$_3$ as a representative manganite, we predict a strong light absorption of this material in the solar spectrum range, resulting in the maximum light-to-electricity energy conversion efficiency up to 33%. We also predict an extraordinary optical linear dichroism and linear birefringence properties of h-TbMnO$_3$ in a broad range of optical frequencies. These results uncover the unexplored potential of hexagonal rare-earth manganites to serve as photovoltaics in solar cells and as absorptive and birefringent light polarizers.Comment: 26 pages, 8 figure

Resistivity and Thermopower of Ni2.19Mn0.81Ga

In this paper, we report results of the first studies on the thermoelectric power (TEP) of the magnetic heusler alloy Ni$_{2.19}$Mn$_{0.81}$Ga. We explain the observed temperature dependence of the TEP in terms of the crystal field (CF) splitting and compare the observed behavior to that of the stoichiometric system Ni$_2$MnGa. The resistivity as a function of temperature of the two systems serves to define the structural transition temperature, T$_M$, which is the transition from the high temperature austenitic phase to low temperatures the martensitic phase. Occurrence of magnetic (Curie-Weiss) and the martensitic transition at almost the same temperature in Ni$_{2.19}$Mn$_{0.81}$Ga has been explained from TEP to be due to changes in the density of states (DOS) at the Fermi level.Comment: 12 pages, 4 figures, Accepted in Physical Review B vol 70, Issue 1

AN EVALUATION OF AN ECONOMIC STRATEGY FOR PREVENTING WATER POLLUTION USING A PHOSPHORUS CONSISTENT TRANSPORTATION MODEL: A CASE OF BROILER LITTER MANAGEMENT

We calculated the profitability of using broiler litter as a source of plant nutrient using a phosphorus consistent litter application rule. We found that each ton of litter can be transferred cost effectively up to 164 miles from the production facilities. The minimum cost phosphorus consistent transportation model developed to meet the nutrient needs of 29 counties in North Alabama revealed that not all the litter can be utilized in the region. The total cost for nutrient supply increased when transportation of litter from heavily surplus counties were prioritized. The effect of chemical fertilizer price change minimally affected the total litter use.Environmental Economics and Policy,

EFFECT OF RISK PERSPECTIVE ON FERTILIZER CHOICE BY SHARECROPPERS

Peanut and corn are two major crops in the tri-state area of the Southeast US, an area encompassing North Florida, Southwest Georgia, and Southeast Alabama. Sharecroppers in this region apply higher amount of input in crop production than the average farmers. We analyzed the behavior of sharecroppers in this region with regard to their fertilizer application decisions. Two hypotheses were formulated and tested based on sharecroppers' fertilizer application decisions: one assuming that sharecroppers are risk averse farmers and the other assuming that sharecroppers are regret minimizers. Our results show that a sharecropper uses different fertilizer treatments when minimizing risk depending on risk perspective and desired income. Sharecroppers who apply more fertilizer to obtain a desired level of income are regret minimizers where as sharecroppers who apply relatively low fertilizer are risk minimizer. At the same desired level of income, a regret minimizer farmer would apply a higher amount of fertilizer than the risk averse farmers. Our analysis revealed that sharecroppers in the Southeast US are regret minimizers as they apply a higher amount of fertilizer than an average farmer on the major crops grown in the region. The result of this study also confirms the result of a previous study in the region which reported that sharecroppers in the region are over capitalized and apply more fertilizer than average farmers.Southeast U.S., Sharecroppers, Regret minimizer, Risk averse, Peanut-Corn rotation, Farm Management, Risk and Uncertainty,

A THEORETICAL DEVELOPMENT AND EMPIRICAL TEST ON THE CONVERGENCE OF AGRICULTURAL PRODUCTIVITY IN THE USA

This study explores the evidence of convergence in the U.S agriculture sector by using the state level total factor productivity (TFP) data. The empirical investigation conducted in this study does not find any evidence of convergence while looking at the state level TFP. However, there seems to be some support for convergence at the regional level. Parametric and nonparametric models indicate significant role of human capital in explaining the regional discrepancies in agriculture productivity across states.Research Methods/ Statistical Methods,

Soil quality as affected by agroforestry and grass buffers in grazed pasture and row crop systems

Title from PDF of title page (University of Missouri--Columbia, viewed on August 27, 2012).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Thesis advisors: Drs. Ranjith P. Udawatta, Stephen H. Anderson and Robert J. KremerIncludes bibliographical references.Vita.M.S. University of Missouri--Columbia 2011."May 2011"Establishment of agroforestry and grass buffers within agroecosystems is believed to improve soil quality. Soil enzyme activities and water stable aggregates have been identified as sensitive soil quality indicators to evaluate early responses to soil management. However, only a few studies compared these parameters among buffers, grazing pastures, and row crop systems. The objective of this study was to compare the activities of selected enzymes, water stable aggregates (WSA), soil organic carbon (SOC), total nitrogen (TN), and bulk density (Db) as soil quality parameters among four management treatments: grazed pasture (GP), agroforestry buffer (AgB), grass buffer (GB) and row crop (RC). Two soil depths (0-10 and 10-20 cm) were analyzed in all treatments for two consecutive years, 2009 and 2010. The enzyme activities, WSA, SOC, TN, and Db were determined by standard procedures. Most of the soil quality indicators were significantly greater in perennial vegetation treatments compared to row crop management indicating that perennial vegetation provides favorable conditions for greater enzyme activities and other soil quality indicators. Although there were numerical variations, the trends in response of quality parameters were consistent between years. Soil enzyme activities were significantly correlated with soil organic carbon content. Assessing changes in selected soil quality indicators appears to be a useful tool to determine soil management effects as well as trends in soil degradation