Lopsidedness in dwarf irregular galaxies

We quantify the amplitude of the lopsidedness, the azimuthal angular asymmetry index, and the concentration of star forming regions, as represented by the distribution of the H$\alpha$ emission, in a sample of 78 late-type irregular galaxies. We bin the observed galaxies in two groups representing blue compact galaxies (BCDs) and low surface brightness dwarf galaxies (LSBs). The light distribution is analysed with a novel algorithm, which allows detection of details in the light distribution pattern. We find that while the asymmetry of the underlying continuum light, representing the older stellar generations, is relatively small, the H$\alpha$ emission is very asymmetric and is correlated in position angle with the continuum light. We test a model of random star formation over the extent of a galaxy by simulating HII regions in artificial dwarf galaxies. The implication is that random star formation over the full extent of a galaxy may be generated in LSB dwarf-irregular galaxies but not in BCD galaxies.Comment: 42 pages, LaTex. Accepted by: MNRAS, 13 Mar 200

An Analysis of a Back Fed Porous Electrode for the Br2/Br Reaction

An experimental analysis of the Br2/Br– redox reaction in a porous back fed ruthenium-coated titanium electrode is described. A mathematical model of the steady-state process is presented. Nonlinear regression of the model against the experimental data gives physically meaningful parameter estimates; these parameters and the model provide a design equation for the porous electrode current as a function of specific surface area, bulk Br2 concentration, average total overpotential, and the Reynolds number. The design equation shows that the back fed electrode could reduce the loss of Br2 across the separator and the ohmic loss in a Zn/Br2 battery

Using Parameter Estimation Techniques with a Simple Model of a Diaphragm-Type Electrolyzer to Predict the Electrical Energy Cost for NaOH Production

Predictions of the electrical energy cost for NaOH production are determined as a function of the independent operating variables and diaphragm characterizing properties. The predictions are based on data from a statistically designed experiment, a simple model of a diaphragm-type electrolyzer, a simple model of the cell voltage losses, and parameter estimation techniques. The data were obtained over a sufficiently large range of operating conditions so that the resulting design equation may be industrially useful. The simple model of the diaphragm is based on the mass transport of the hydroxyl ion, a linear potential gradient, and is presented in terms of measurable diaphragm properties.These properties are the thickness of the diaphragm (t) and a resistivity ratio, /0, where is the resistivity of the diaphragm filled with electrolyte and 0 is the resistivity of the electrolyte (this ratio may come to be known as the MacMullin number, NM). It is shown that, according to the model of the cell, the caustic yield or current efficiency of the diaphragm cell depends on the product of NM and t and not on each separately. The simple model of the cell voltage considers the diaphragm voltage drop, anode and cathode kinetics, and the bubble-filled brine-gap voltage drop. Parameter estimation techniques are used to determine the best values of the diffusion coefficient, average specific conductivity, exchange current densities, and transfer coefficients; these parameters and the simple models provide a design equation for the electrical energy cost of NaOH production using a diaphragm cell. The design equation is used to predict aminimum electrical-energy cost at a particular NMt

Simple Models for Diaphragm-Type Chlorine/Caustic Cells II. Effect of Acidic Anolyte on Steady-State Caustic Yield

A simple steady-state model of a diaphragm-type chlorine/caustic cell in which the diaphragm is divided into two regions by a homogeneous acid-base reaction is presented. The location of the reaction affects significantly the caustic yield and effluent concentration. The model is used to predict the location of this reaction as a function of the operating variables, the physical constants, and three measurable properties of the diaphragm. These measurable properties are the MacMullin number or resistivity ratio of electrolyte-filled diaphragm relative to the electrolyte, the Darcy\u27s law diaphragmpermeability, and the diaphragm thickness. The model is used to predict a maximum in the relationship between the caustic yield and caustic effluent concentration. The model predictions are compared with experimental data by using parameter estimation techniques to determine the diffusion coefficients of hydroxyl and hydrogen ions and the average specific conductivity of the electrolyte within the diaphragm during operation of the cell

Mechanism of Pitting Corrosion Prevention by Nitrite in Carbon Steel Exposed to Dilute Salt Solutions

The research has developed a broad fundamental understanding of the inhibition action of nitrite ions in preventing nitrate pitting corrosion of carbon steel tanks containing high-level radioactive waste. This fundamental understanding can be applied to specific situations during waste removal for permanent disposition and waste tank closure to ensure that the tanks are maintained safely. The results of the research provide the insight necessary to develop solutions that prevent further degradation

Simple Models for Diaphragm-Type Chlorine/Caustic Cells I. Dynamic Behavior

A simple model of the dynamic behavior of a diaphragm-type chlorine/caustic cell is presented. The model is based upon measurable diaphragm properties and the mass transfer of hydroxyl ion through the diaphragm. The anolyte is modeled simply as a region in which the OH– ion concentration is fixed, the diaphragm is modeled as a plug-flow reactor with an electrochemical reaction occurring at the catholyte/diaphragm interface where the cathode is placed, and the catholyte is modeled as a completely stirred flow reactor. Analytical integration of the governing equations for thesemodels yields two mathematical expressions: one for the concentration distribution of hydroxyl ion within the diaphragm and one for the effluent concentration. Both of these expressions are functions of time, independent operating variables, diaphragm properties, and physical constants. They are used to show how the concentration distribution ofOH– within the diaphragm and the cell effluent change when subjected to a step change in the current density. Also presented is a numerical method of solution for the model equations to predict the required change of the cell head subject to an arbitrary time-dependent change in the current density at a fixed cell effluent concentration

A Model for the Galvanostatic Deposition of Nickel Hydroxide

A mathematical model is presented for the galvanostatic deposition of Ni(OH)2 films in stagnant Ni(NO3)2 solutions. The objective is to quantify the anomalous deposition behavior reported previously in which the utilization of the electrochemically generated OH– species decreased drastically as the concentration of Ni(NO3)2 increased beyond 0.1 M. For example as the Ni(NO3)2 concentration increased from 0.1 to 2.0 M, the deposition rate decreased by a factor of ten at 2.5 mA/cm2. At this high ratio of concentration to current density, a comparison with Faraday\u27s law indicates that only 10% of the OH– species generated at the surface led to deposition. It has been proposed that the inefficient use of electrochemically generated OH– species is due to the presence of Ni4(OH) as an intermediate in the deposition process. As the bulk Ni(NO3)2 concentration increases, the concentration of Ni4(OH) at the electrode surface increases. A high concentration of the intermediate results in an increase in the diffusion rate of the species away from the electrode surface and thus a decrease in the deposition rate. Here, this hypothesis is tested by developing a model which includes the generation of OH– from the electrochemical reduction of nitrate to ammonia and the diffusion and migration of Ni2+, NO, OH–, H+, and Ni4(OH). The model predictions agree well with previously reported mass deposition data collected using an electrochemical quartz crystal microbalance at different currents and over a range of Ni(NO3)2 concentrations. The present work confirms the role that Ni4(OH) plays in the deposition process and provides a fundamental framework for understanding the electrochemical impregnation of nickel electrodes

Current Status of the Plains Pocket Mouse, Perognathus flavescens, in Iowa

Published and unpublished accounts of the plains pocket mouse (Perognathus flavescens) were utilized to document the existence of extant populations and to summarize and report additional data about the biology of this state endangered Iowa species. Populations of P. flavescens exist in western (Harrison, Monona, and Plymouth counties) and extreme eastern (adjacent portions of Louisa and Muscatine counties) Iowa, the latter of which represents the eastern-most record for the species in North America. In addition, we document a new locality for P. flavescens from the interior of the state (Benton County). All known populations of P. flavescens in Iowa occur in grassland habitats on well-drained substrates (i.e., loess, sandy loam, and sandy soils). Reproductive data suggested that P. flavescens in Iowa have at least two litters (early spring and late summer) of three to eight young. We hope this paper will stimulate additional research that will lead to a better understanding of the general distribution and biology of P. flavescens in Iowa