Electrochemical Time of Flight for Rapid and Direct Measurement of Diffusion Coefficients

The determination of diffusion coefficients is of fundamental importance to the understanding of electrochemistry and sensors. Developing a method by which diffusion coefficients of Red/ox active analytes can be determined quickly and elegantly, would be a great advancement over presently accepted methods. This dissertation reports the reviving electrochemical time of flight (ETOF), and developing a method that allows for empirical determination of diffusion coefficients from a single measurement. ETOF is a generate and detect experiment where the time an electrochemically generated species takes to transit a known distance is measured and related to the diffusion coefficient of the species. The determined diffusion coefficient of ferricyanide, 7.3(±0.7) x 10-6 cm2/s, was within the 95% confidence interval of the literature value, using the traditional ETOF data treatment. In this dissertation a new treatment of the data, the Moldenhauer treatment, where a diffusional calibration curve is constructed using multiple species of known diffusion coefficient and measuring their transit times at a set distance. The calibration curve constructed in aqueous solutions found the diffusion coefficient of ruthenium(II) hexamine to be within the 95% confidence interval of what has been reported in the literature. The same calibration was also used to determine diffusion coefficients of aqueous probe molecules in a more viscous solution of 20% v/v ethylene glycol and water. Computational modeling was used to further optimize generator pulse widths to allow for a greater linear range of determineable diffusion coefficients. It was shown that an empirically determined aqueous calibration can be used to determine diffusion coefficients in organic solvents. The diffusion coefficient of ferrocene was determined to be 2.4(±0.1) x10-5 cm2/s after modeling directed optimum generator pulse widths. In addition diffusion coefficients were determined for tetrabutylammonium dioxovanadium(V) dipicolinate (3.9(±0.2) x 10─6 cm2/s), and ruthenium (II) bisbipyridine dichloride (9.3(±0.4)x10─6 cm2/s), which do not have published diffusion coefficients presently. Int the future, this same method could be used to determine diffusion coefficients in membranes and complex solvents such as ionic liquids

Figures of merit and constraints from testing General Relativity using the latest cosmological data sets including refined COSMOS 3D weak lensing

We use cosmological constraints from current data sets and a figure of merit (FoM) approach to probe any deviations from general relativity (GR) at cosmological scales. The FoM approach is used to study the constraining power of various combinations of data sets on modified gravity (MG) parameters. We use recently refined HST-COSMOS weak-lensing tomography data, ISW-galaxy cross correlations from 2MASS and SDSS LRG surveys, matter power spectrum from SDSS-DR7 (MPK), WMAP7 temperature and polarization spectra, BAO from 2DF and SDSS-DR7, and Union2 compilation of supernovae, in addition to other bounds from H_0 measurements and BBN. We use 3 parametrizations of MG parameters that enter the perturbed field equations. In order to allow for variations with redshift and scale, the first 2 parametrizations use recently suggested functional forms while the third is based on binning methods. Using the first parametrization, we find that CMB + ISW + WL provides the strongest constraints on MG parameters followed by CMB+WL or CMB+MPK+ISW. Using the second parametrization or binning methods, CMB+MPK+ISW consistently provides some of the strongest constraints. This shows that the constraints are parametrization dependent. We find that adding up current data sets does not improve consistently uncertainties on MG parameters due to tensions between best-fit MG parameters preferred by different data sets. Furthermore, some functional forms imposed by the parametrizations can lead to an exacerbation of these tensions. Next, unlike some studies that used the CFHTLS lensing data, we do not find any deviation from GR using the refined HST-COSMOS data, confirming previous claims in those studies that their result may have been due to some systematic effect. Finally, we find in all cases that the values corresponding to GR are within the 95% confidence level contours for all data set combinations. (abridged)Comment: 18 pages, 6 figures, matches version published in PR

Principles and methods of wind-erosion control in Iowa

Wind erosion in Iowa has been increasing in frequency and intensity with the increase in acreage of row crops and consequent increase in fall-plowed acres. This erosion has attracted widespread attention because blowing dust has created a hazard to health and safety. This bulletin is a report of research conducted in areas where wind erosion has been a problem for many years and the application of the findings in Iowa.https://lib.dr.iastate.edu/specialreports/1058/thumbnail.jp

What About Continuous Corn?

Interest in continuous corn in Iowa has been g rowing for several years. And increasing numbers of farmers have been trying it out on their own. Here\u27s a report on the results of our Iowa tests with continuous corn

Using Rainfall Records as Guides to Predict Yields of Cotton on Drylands of the High and Rolling Plains of Texas.

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The influence of nitrogen and phosphorus ferilization on nutrient status and profitability of Bromegrass on Ida soils

This study was undertaken to determine the profitability and the feasibility of fertilizing bromegrass for grazing in the Monona-Ida-Hamburg soil association area. This area is well adapted to growing forage crops. Because of the high content of calcium and potassium, alfalfa grows well if phosphorus is applied. Bromegrass is able in some way to get nitrogen from alfalfa, and the two crops grow well together. The bloat danger in pasturing alfalfa or bromegrass-alfalfa mixtures, however, is well known to cattlemen in the area. Many believe the cost of nitrogen fertilizer to maintain productivity of bromegrass pastures is less than the cost of losses from bloat on bromegrass-alfalfa pastures. The profitability of fertilizing bromegrass stands is examined in Part I of the study. The feasibility is examined in Part II. In Part I, returns at three levels of nitrogen cost and beef price and at three conversion ratios of forage to beef are calculated on the basis of experimental yields

Approximating Node-Weighted k-MST on Planar Graphs

We study the problem of finding a minimum weight connected subgraph spanning at least $k$ vertices on planar, node-weighted graphs. We give a (4+\eps)-approximation algorithm for this problem. We achieve this by utilizing the recent LMP primal-dual $3$-approximation for the node-weighted prize-collecting Steiner tree problem by Byrka et al (SWAT'16) and adopting an approach by Chudak et al. (Math.\ Prog.\ '04) regarding Lagrangian relaxation for the edge-weighted variant. In particular, we improve the procedure of picking additional vertices (tree merging procedure) given by Sadeghian (2013) by taking a constant number of recursive steps and utilizing the limited guessing procedure of Arora and Karakostas (Math.\ Prog.\ '06). More generally, our approach readily gives a (\nicefrac{4}{3}\cdot r+\eps)-approximation on any graph class where the algorithm of Byrka et al.\ for the prize-collecting version gives an $r$-approximation. We argue that this can be interpreted as a generalization of an analogous result by K\"onemann et al. (Algorithmica~'11) for partial cover problems. Together with a lower bound construction by Mestre (STACS'08) for partial cover this implies that our bound is essentially best possible among algorithms that utilize an LMP algorithm for the Lagrangian relaxation as a black box. In addition to that, we argue by a more involved lower bound construction that even using the LMP algorithm by Byrka et al.\ in a \emph{non-black-box} fashion could not beat the factor \nicefrac{4}{3}\cdot r when the tree merging step relies only on the solutions output by the LMP algorithm