Investigation of clay and neutron absorbers’ roles in the genesis and evolution of Oklo natural nuclear reactors

International audienceSince their discovery, the Oklo natural nuclear reactors were subject of many detailed field studies, sample analysis and criticality simulations. The present article is dedicated to advanced simulations of Oklo cores using a custom Python code to generalize and automate MCNP criticality calculations. The impacts of both the initial neutron absorbers and the clay fraction, which define the initial and evolving mineralogical environment, were studied by means of parametric simulations

Elastic Deformation in Ceria Nanorods via a Fluorite-to-Rutile Phase Transition

Atomistic simulations reveal that ceria nanorods, under uniaxial tension, can accommodate over 6% elastic deformation. Moreover, a reversible fluorite-to- rutile phase change occurs above 6% strain for a ceria nanorod that extends along [110]. We also observe that during unloading the stress increases with decreasing strain as the rutile reverts back to fluorite. Ceria nanorods may find possible application as vehicles for elastic energy storage

Aligning and Labeling Genomes Under the Duplication-Loss Model

Abstract. In this paper we investigate the complexity of two combinatorial problems related to genome alignment, a recent approach to genome comparison based on a duplication-loss model of evolution. The first combinatorial problem, Duplication-Loss Alignment, aims to align two genomes and to explain the unaligned part of the genomes as duplications and losses. The problem has been recently shown to be NP-hard, even when each gene has at most five occurrences in each genome. Here, we improve this result by showing that Duplication-Loss Alignment is APX-hard even if the number of occurrences of a gene inside a genome is bounded by 2. Then we consider a second combinatorial problem, Minimum Relabeling Alignment, and we show that it is equivalent to Minimum Feedback Vertex Set on Direct Graph, hence implying that the problem is APX-hard, is fixed-parameter tractable and approximable within factor O(log|X|loglog|X|), where X is the aligned genome considered by Minimum Relabeling Alignment.