The anodic dissolution of magnesium in aqueous solutions

The anodic dissolution of magnesium was studied in MgCl2-KC1 and MgBr2-KBr mixtures at 25, 40, and 55 °C. The parameters of the study were current density, concentration of magnesium ion, and temperature. The concentration of magnesium ions was varied from 0.001 to 1 N holding the ionic strength constant at 1.5. The weight loss of magnesium from the electrode during electrolysis was determined by weighing the electrode both before and after electrolysis. The current was measured with a sensitive milliammeter. The range of the current densities was varied from 0.001 to 0.1 amps·cm-2. The apparent valence of magnesium ions going into solution was determined. The following was concluded: The apparent valence of magnesium dissolving anodically is decreased rapidly as current density is increased at current densities below 0.03 amps·cm-2. From 0.03 to 0.1 amps·cm-2, the apparent valence decreases slowly with increasing density. The effect of concentration of magnesium ions and temperature on the apparent valence of magnesium dissolving anodically in KCl-MgCl2 and KBr-MgBr2 mixtures is small. The apparent valence of magnesium dissolving in 1 N MgCl2 and MgBr2 solutions has a much more pronounced temperature and current density effect at low current densities. The apparent valence-current density plots for the anodic dissolution of magnesium can be separated into two regions where there exists linear relationships between them. The potential measurements of magnesium dissolving anodically under similar conditions led to the following conclusions: The overpotential is very slightly affected by temperature and concentration, except in 1 N MgCl2 and MgBr2 solutions. The electrode is not appreciably polarized at current densities below 0.03 amps·cm-2. Above 0.03amps·cm-2 the electrode polarizes rapidly indicating passivation. On the basis of the above, it is concluded that the behavior of magnesium is consistent with the model proposed by Sun in which the anodic dissolution consists of three simultaneous processes, an electrochemical reaction, local corrosion, and disintegration. The deviation of the valence of the magnesium ions from the normal valence, i.e., deviation from Faraday\u27s law, is accounted for by local corrosion and disintegration. A mathematical model is derived that gives the observed influence of current density --Abstract, pages iii-iv

Robust portfolio management with multiple financial analysts

Portfolio selection theory, developed by Markowitz (1952), is one of the best known and widely applied methods for allocating funds among possible investment choices, where investment decision making is a trade-off between the expected return and risk of the portfolio. Many portfolio selection models have been developed on the basis of Markowitz’s theory. Most of them assume that complete investment information is available and that it can be accurately extracted from the historical data. However, this complete information never exists in reality. There are many kinds of ambiguity and vagueness which cannot be dealt with in the historical data but still need to be considered in portfolio selection. For example, to address the issue of uncertainty caused by estimation errors, the robust counterpart approach of Ben-Tal and Nemirovski (1998) has been employed frequently in recent years. Robustification, however, often leads to a more conservative solution. As a consequence, one of the most common critiques against the robust counterpart approach is the excessively pessimistic character of the robust asset allocation. This thesis attempts to develop new approaches to improve on the respective performances of the robust counterpart approach by incorporating additional investment information sources, so that the optimal portfolio can be more reliable and, at the same time, achieve a greater return. [Continues.