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Pyrite oxidation under initially neutral pH conditions and in the presence of Acidithiobacillus ferrooxidans and micromolar hydrogen peroxide
Hydrogen peroxide (H2O2) at a micromolar level played a role in the microbial surface oxidation of pyrite crystals under initially neutral pH. When the mineral-bacteria system
was cyclically exposed to 50 μM H2O2, the colonization of Acidithiobacillus ferrooxidans onto the mineral surface was markedly enhanced, as compared to the control(no added H2O2). This can be attributed to the effects of H2O2 on increasing the roughness of the mineral surfaces, as well as the acidity and Fe2+ concentration at the mineral-solution interfaces. All of these effects tended to create more favourable nanoto micro-scale environments in the mineral surfaces for the cell adsorption. However, higher H2O2 levels inhibited the attachment of cells onto the mineral surfaces, possibly due to the oxidative stress in the bacteria when they approached the mineral surfaces
where high levels of free radicals are present as a result of Fenton-like reactions. The more aggressive nature of H2O2 as an oxidant caused marked surface flaking of the
mineral surface. The XPS results suggest that H2O2 accelerated the oxidation of pyrite-S and consequently facilitated the overall corrosion cycle of pyrite surfaces. This was accompanied by pH drop in the solution in contact with the pyrite cubes
Iteration Complexity Analysis of Multi-Block ADMM for a Family of Convex Minimization without Strong Convexity
The alternating direction method of multipliers (ADMM) is widely used in
solving structured convex optimization problems due to its superior practical
performance. On the theoretical side however, a counterexample was shown in [7]
indicating that the multi-block ADMM for minimizing the sum of
convex functions with block variables linked by linear constraints may
diverge. It is therefore of great interest to investigate further sufficient
conditions on the input side which can guarantee convergence for the
multi-block ADMM. The existing results typically require the strong convexity
on parts of the objective. In this paper, we present convergence and
convergence rate results for the multi-block ADMM applied to solve certain
-block convex minimization problems without requiring strong
convexity. Specifically, we prove the following two results: (1) the
multi-block ADMM returns an -optimal solution within
iterations by solving an associated perturbation to the
original problem; (2) the multi-block ADMM returns an -optimal
solution within iterations when it is applied to solve a
certain sharing problem, under the condition that the augmented Lagrangian
function satisfies the Kurdyka-Lojasiewicz property, which essentially covers
most convex optimization models except for some pathological cases.Comment: arXiv admin note: text overlap with arXiv:1408.426
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