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.

An Iterative Ensemble Kalman Filter for Multiphase Fluid Flow Data Assimilation

Abstract: Summary The dynamical equations for multiphase flow in porous media are highly non-linear and the number of variables required to characterize the medium is usually large, often two or more variables per simulator gridblock. Neither the extended Kalman filter nor the ensemble Kalman filter is suitable for assimilating data or for characterizing uncertainty for this type of problem. Although the ensemble Kalman filter handles the nonlinear dynamics correctly during the forecast step, it sometimes fails badly in the analysis (or updating) of saturations. This paper focuses on the use of an iterative ensemble Kalman filter for data assimilation in nonlinear problems, especially of the type related to multiphase flow in porous media. Two issues are key: (1) iteration to enforce constraints and (2) ensuring that the resulting ensemble is representative of the conditional pdf (i.e. that the uncertainty quantification is correct). The new algorithm is compared to the ensemble Kalman filter on several highly nonlinear example problems, and shown to be superior in the prediction of uncertainty.

Evaluation of 11 terrestrial carbon–nitrogen cycle models against observations from two temperate Free‐Air CO2 Enrichment studies

Abstract: We analysed the responses of 11 ecosystem models to elevated atmospheric [CO2] (eCO(2)) at two temperate forest ecosystems (Duke and Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) experiments) to test alternative representations of carbon (C)-nitrogen (N) cycle processes. We decomposed the model responses into component processes affecting the response to eCO(2) and confronted these with observations from the FACE experiments. Most of the models reproduced the observed initial enhancement of net primary production (NPP) at both sites, but none was able to simulate both the sustained 10-yr enhancement at Duke and the declining response at ORNL: models generally showed signs of progressive N limitation as a result of lower than observed plant N uptake. Nonetheless, many models showed qualitative agreement with observed component processes. The results suggest that improved representation of above-ground-below-ground interactions and better constraints on plant stoichiometry are important for a predictive understanding of eCO(2) effects. Improved accuracy of soil organic matter inventories is pivotal to reduce uncertainty in the observed C-N budgets. The two FACE experiments are insufficient to fully constrain terrestrial responses to eCO(2), given the complexity of factors leading to the observed diverging trends, and the consequential inability of the models to explain these trends. Nevertheless, the ecosystem models were able to capture important features of the experiments, lending some support to their projections. (Less)

The effects of daily exercise on susceptibility to sudden cardiac death.

Abstract: The purpose of this study was to investigate the effects of daily exercise on susceptibility to sudden cardiac death. A 2 min coronary occlusion was initiated during the last minute of an exercise stress test and continued for 1 min after cessation of exercise in chronically instrumented dogs with a healed anterior wall myocardial infarction. Thirteen dogs developed ventricular fibrillation (VF; susceptible), while five did not (resistant). Before the exercise plus ischemia test, the baroreflex was evaluated with a bolus injection of phenylephrine (10 micrograms/kg). The changes in heart rate caused by a 30 mm Hg increase in systolic arterial pressure as well as the slopes of either heart rate or RR interval plotted against systolic arterial pressure were significantly lower in dogs that developed VR (resistant, -49.6 +/- 7.8; susceptible, -15.3 +/- 6.4 beats/min; p less than .001). Four resistant and eight susceptible animals were then placed on a 6 week daily exercise program, while eight susceptible dogs had an equal period of rest. At the end of the 6 week period the exercise plus ischemia test was repeated; no susceptible animal that performed daily exercise developed VF, and all but one of the rested animals did. Daily exercise improved baroreflex control of heart rate in the susceptible group but not in the resistant group. Rest did not alter baroreflex function (change in heart rate after 30 mm Hg increase in systolic arterial pressure: after 6 weeks of exercise, resistant -43.3 +/- 18.9 beats/min, susceptible -60.8 +/- 16.6 beats/min; after 6 weeks of rest, susceptible 27.4 +/- 11.0 beats/min). We conclude that daily exercise prevents VF induced by acute myocardial ischemia in a subpopulation of dogs that were previously identified as susceptible to sudden cardiac death. Exercise also altered the autonomic control of the heart, possibly decreasing sympathetic and/or increasing parasympathetic tone.(ABSTRACT TRUNCATED AT 250 WORDS)