Density functional calculations of the formation and migration enthalpies of monovacancies in Ni: Comparison of local and nonlocal approaches

We examine in this work the potential and the functional to be used in a density functional theory approach in order to describe correctly the formation and migration energies of monovacancies in nickel. As the formation enthalpy is not well-known experimentally at 0 K, we choose in a first step to determine some structural, magnetic, and elastic properties of the bulk, which are well-established experimentally. The comparison between both approaches, i.e., the local spin density approximation LSDA and the generalized gradient approximation GGA exchange-correlation functionals is analyzed. We conclude that the contribution of nonlocal GGA terms in order to describe correctly the electronic density is necessary to determine the formation and migration enthalpies and activation energy of monovacancy. The calculated formation Hv f and migration Hv m enthalpies differ significantly between both approaches. The overestimation of the LSDA approximation is of 0.25 eV for Hv f and of 0.23 eV for Hv m with respect to the GGA one, leading to a gap of 0.48 eV between both methods for the activation energy Q1. We show that the GGA results are comparable with experimental data if the thermal expansion contribution is taken into account through the lattice parameter variation. Finally, it is shown that the activation energy is nearly independent of the thermal expansion effects; thus we can expect that the curvature of the Arrhenius plot of the diffusion factor near the melting point is essentially due to the contribution of divacancies

Chloroplast DNA sequence of the green alga <it>Oedogonium cardiacum </it>(Chlorophyceae): Unique genome architecture, derived characters shared with the Chaetophorales and novel genes acquired through horizontal transfer

<p>Abstract</p> <p>Background</p> <p>To gain insight into the branching order of the five main lineages currently recognized in the green algal class Chlorophyceae and to expand our understanding of chloroplast genome evolution, we have undertaken the sequencing of chloroplast DNA (cpDNA) from representative taxa. The complete cpDNA sequences previously reported for <it>Chlamydomonas </it>(Chlamydomonadales), <it>Scenedesmus </it>(Sphaeropleales), and <it>Stigeoclonium </it>(Chaetophorales) revealed tremendous variability in their architecture, the retention of only few ancestral gene clusters, and derived clusters shared by <it>Chlamydomonas </it>and <it>Scenedesmus</it>. Unexpectedly, our recent phylogenies inferred from these cpDNAs and the partial sequences of three other chlorophycean cpDNAs disclosed two major clades, one uniting the Chlamydomonadales and Sphaeropleales (CS clade) and the other uniting the Oedogoniales, Chaetophorales and Chaetopeltidales (OCC clade). Although molecular signatures provided strong support for this dichotomy and for the branching of the Oedogoniales as the earliest-diverging lineage of the OCC clade, more data are required to validate these phylogenies. We describe here the complete cpDNA sequence of <it>Oedogonium cardiacum </it>(Oedogoniales).</p> <p>Results</p> <p>Like its three chlorophycean homologues, the 196,547-bp <it>Oedogonium </it>chloroplast genome displays a distinctive architecture. This genome is one of the most compact among photosynthetic chlorophytes. It has an atypical quadripartite structure, is intron-rich (17 group I and 4 group II introns), and displays 99 different conserved genes and four long open reading frames (ORFs), three of which are clustered in the spacious inverted repeat of 35,493 bp. Intriguingly, two of these ORFs (<it>int </it>and <it>dpoB</it>) revealed high similarities to genes not usually found in cpDNA. At the gene content and gene order levels, the <it>Oedogonium </it>genome most closely resembles its <it>Stigeoclonium </it>counterpart. Characters shared by these chlorophyceans but missing in members of the CS clade include the retention of <it>psaM</it>, <it>rpl32 </it>and <it>trnL</it>(caa), the loss of <it>petA</it>, the disruption of three ancestral clusters and the presence of five derived gene clusters.</p> <p>Conclusion</p> <p>The <it>Oedogonium </it>chloroplast genome disclosed additional characters that bolster the evidence for a close alliance between the Oedogoniales and Chaetophorales. Our unprecedented finding of <it>int </it>and <it>dpoB </it>in this cpDNA provides a clear example that novel genes were acquired by the chloroplast genome through horizontal transfers, possibly from a mitochondrial genome donor.</p

Extreme faint flux imaging with an EMCCD

An EMCCD camera, designed from the ground up for extreme faint flux imaging, is presented. CCCP, the CCD Controller for Counting Photons, has been integrated with a CCD97 EMCCD from e2v technologies into a scientific camera at the Laboratoire d'Astrophysique Experimentale (LAE), Universite de Montreal. This new camera achieves sub-electron read-out noise and very low Clock Induced Charge (CIC) levels, which are mandatory for extreme faint flux imaging. It has been characterized in laboratory and used on the Observatoire du Mont Megantic 1.6-m telescope. The performance of the camera is discussed and experimental data with the first scientific data are presented.Comment: 33 pages, 17 figures, accepted for publication in PAS