University of Oklahoma

About: University of Oklahoma is a education organization based out in Norman, Oklahoma, United States. It is known for research contribution in the topics: Population & Radar. The organization has 25269 authors who have published 52609 publications receiving 1821706 citations. The organization is also known as: OU & Oklahoma University.

Scaling of an anomalous metal-insulator transition in a two-dimensional system in silicon at B =0

Abstract: We have studied the temperature dependence of resistivity, \ensuremath{\rho}, for a two-dimensional electron system in silicon at low electron densities ${\mathit{n}}_{\mathit{s}}$\ensuremath{\sim}${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, near the metal-insulator transition The resistivity was empirically found to scale with a single parameter ${\mathit{T}}_{0}$, which approaches zero at some critical electron density ${\mathit{n}}_{\mathit{c}}$ and increases as a power ${\mathit{T}}_{0}$\ensuremath{\propto}\ensuremath{\Vert}${\mathit{n}}_{\mathit{s}}$-${\mathit{n}}_{\mathit{c}}$${\mathrm{\ensuremath{\Vert}}}^{\mathrm{\ensuremath{\beta}}}$ with \ensuremath{\beta}=16\ifmmode\pm\else\textpm\fi{}01 both in metallic (${\mathit{n}}_{\mathit{s}}$g${\mathit{n}}_{\mathit{c}}$) and insulating (${\mathit{n}}_{\mathit{s}}$${\mathit{n}}_{\mathit{c}}$) regions This dependence was found to be sample independent We have also studied the diagonal resistivity at Landau-level filling factor \ensuremath{ u}=3/2, where the system is known to be in a true metallic state at high magnetic field and in an insulating state at low magnetic field The temperature dependencies of resistivity at B=0 and \ensuremath{ u}=3/2 were found to be identical These behaviors suggest a true metal-insulator transition in the two-dimensional electron system in silicon at B=0, in contrast with the well-known scaling theory

Metagenomic insights into evolution of a heavy metal-contaminated groundwater microbial community

Abstract: Understanding adaptation of biological communities to environmental change is a central issue in ecology and evolution. Metagenomic analysis of a stressed groundwater microbial community reveals that prolonged exposure to high concentrations of heavy metals, nitric acid and organic solvents ( approximately 50 years) has resulted in a massive decrease in species and allelic diversity as well as a significant loss of metabolic diversity. Although the surviving microbial community possesses all metabolic pathways necessary for survival and growth in such an extreme environment, its structure is very simple, primarily composed of clonal denitrifying gamma- and beta-proteobacterial populations. The resulting community is overabundant in key genes conferring resistance to specific stresses including nitrate, heavy metals and acetone. Evolutionary analysis indicates that lateral gene transfer could have a key function in rapid response and adaptation to environmental contamination. The results presented in this study have important implications in understanding, assessing and predicting the impacts of human-induced activities on microbial communities ranging from human health to agriculture to environmental management, and their responses to environmental changes.

Labile, recalcitrant, and microbial carbon and nitrogen pools of a tallgrass prairie soil in the US Great Plains subjected to experimental warming and clipping

Abstract: Carbon (C) and nitrogen (N) fluxes are largely controlled by the small but highly bio-reactive, labile pools of these elements in terrestrial soils, while long-term C and N storage is determined by the long-lived recalcitrant fractions. Changes in the size of these pools and redistribution among them in response to global warming may considerably affect the long-term terrestrial C and N storage. However, such changes have not been carefully examined in field warming experiments. This study used sulfuric acid hydrolysis to quantify changes in labile and recalcitrant C and N fractions of soil in a tallgrass prairie ecosystem that had been continuously warmed with or without clipping for about 2.5 years. Warming significantly increased labile C and N fractions in the unclipped plots, resulting in increments of 373 mg C kg −1 dry soil and 15 mg N kg −1 dry soil, over this period whilst clipping significantly decreased such concentrations in the warmed plots. Warming also significantly increased soil microbial biomass C and N in the unclipped plots, and increased ratios of soil microbial/labile C and N, indicating an increase in microbial C- and N-use efficiency. Recalcitrant and total C and N contents were not significantly affected by warming. For all measured pools, only labile and microbial biomass C fractions showed significant interactions between warming and clipping, indicating the dependence of the warming effects on clipping. Our results suggest that increased soil labile and microbial C and N fractions likely resulted indirectly from warming increases in plant biomass input, which may be larger than warming-enhanced decomposition of labile organic compounds.

Computational survey of univariate and multivariate learning curve models

Abstract: A computational survey of the various univariate and multivariate learning curve models that have evolved over the past several years is presented. Discussions are presented to show how the models might be used for cost analysis or productivity assessment in engineering management. A computational experiment comparing a univariate model to a bivariate model is presented. While the bivariate model provides only a slightly better fit than the univariate model, it does provide more detailed information about the factor interactions, and better utilization of available data. The results of the computational experiment can be generalized for the appropriateness of multivariate models. >

Lipoproteins as mediators for the effects of alcohol consumption and cigarette smoking on cardiovascular mortality: results from the lipid research clinics follow-up study

Abstract: Because alcohol consumption is associated with increased high density lipoprotein (HDL) cholesterol and decreased low density lipoprotein (LDL) cholesterol, and cigarette smoking is associated with lower HDL cholesterol and higher LDL cholesterol, there has been speculation that the protective effect of moderate alcohol consumption and/or the noxious effect of cigarette smoking for cardiovascular disease might be mediated in large part by a lipoprotein mechanism. The authors examined this question in a prospective study of 7,461 men and women in 10 North American populations initially seen in 1972-1976 and followed for an average of 8.5 years. Moderate alcohol consumption was weakly protective for cardiovascular disease, while cigarette smoking was strongly and significantly associated with cardiovascular disease mortality. As expected, LDL cholesterol was positively related and HDL cholesterol was inversely related to cardiovascular disease mortality. However, multivariable analysis of cardiovascular disease mortality alternately excluding and including HDL cholesterol and LDL cholesterol as covariates indicated that the effect of alcohol consumption on cardiovascular disease mortality was independent of an LDL cholesterol pathway and only partially mediated by an HDL cholesterol pathway, while the effect of cigarette smoking was independent of both the HDL cholesterol and LDL cholesterol pathways, suggesting alternative biologic mechanisms of action for both alcohol consumption and cigarette smoking on cardiovascular disease.