Charge Distribution Near Oxygen Vacancies in Reduced Ceria

Understanding the electronic charge distribution around oxygen vacancies in transition metal and rare earth oxides is a scientific challenge of considerable technological importance. We show how significant information about the charge distribution around vacancies in cerium oxide can be gained from a study of high resolution crystal structures of higher order oxides which exhibit ordering of oxygen vacancies. Specifically, we consider the implications of a bond valence sum analysis of Ce$_{7}$O$_{12}$ and Ce$_{11}$O$_{20}$. To illuminate our analysis we show alternative representations of the crystal structures in terms of orderly arrays of co-ordination defects and in terms of flourite-type modules. We found that in Ce$_{7}$O$_{12}$, the excess charge resulting from removal of an oxygen atom delocalizes among all three triclinic Ce sites closest to the O vacancy. In Ce$_{11}$O$_{20}$, the charge localizes on the next nearest neighbour Ce atoms. Our main result is that the charge prefers to distribute itself so that it is farthest away from the O vacancies. This contradicts \emph{the standard picture of charge localisation} which assumes that each of the two excess electrons localises on one of the cerium ions nearest to the vacancy. This standard picture is assumed in most calculations based on density functional theory (DFT). Based on the known crystal structure of Pr$_{6}$O$_{11}$, we also predict that the charge in Ce$_{6}$O$_{11}$ will be found in the second coordination shell of the O vacancy. Although this review focuses on bulk cerium oxides our approach to characterising electronic properties of oxygen vacancies and the physical insights gained should also be relevant to surface defects and to other rare earth and transition metal oxides.Comment: 20 pages, 23 figures. The replacement file has a new format for the figures are the document layout but no change in content. v3 has the following main changes: 1. The abstract and introduction were extensively revised. 2. Sec. IV was removed. 3. The Conclusion was rewritte

Christianity, ‘supernatural’ beliefs and COVID-19

COVID-19 arguably had far-reaching implications for Christianity and the church as an institution. Issues around social distancing and lockdown directly impacted articulation and religious expression, while understanding of the pandemic and the virus were mediated through constructions of religio-spiritual beliefs. Given this, the study sought to explore some neo-Pentecostal church leaders’ messages in South Africa regarding the novel coronavirus or COVID-19, what this meant to their followers and the associated implications for the spread and effects of COVID-19. Methodologically, the researcher iewed and listened to uploaded YouTube video clips of news related to the church and COVID-19, uploaded bymedia outlets and the neo-Pentecostal church leaders themselves as well as online newspaper reports from the period 2 March to 19 June 2020. The findings of the study reveal that neo-Pentecostal church leaders attributed the origins of SARS-COV-2 to “evil” spirits. Neo-Pentecostal church leaders had mixed messages on the possible cure for COVID-19, with some emphasising miracles as the panacea for COVID-19, and a minority believing that God exhibits his power through epidemiologists. Prayer was also viewed as a tool for Christians to protect themselves from contracting COVID-19 through the invocation of divine powers. The paper concludes that the pervasive influence of church leaders and their emphasis onspiritual remedies such as prayer and miracles may have given Pentecostal followers a false sense of security, which might have affected their awareness of COVID-19

Observation of the Halo of NGC 3077 Near the "Garland" Region Using the Hubble Space Telescope

We report the detection of upper main sequence stars and red giant branch stars in the halo of an amorphous galaxy, NGC3077. The observations were made using Wide Field Planetary Camera~2 on board the Hubble Space Telescope. The red giant branch luminosity function in I-band shows a sudden discontinuity at I = 24.0 +- 0.1 mag. Identifying this with the tip of the red giant branch (TRGB), and adopting the calibration provided by Lee, Freedman, & Madore (1993) and the foreground extinction of A_B = 0.21 mag, we obtain a distance modulus of (m-M)_0 = 27.93 +- 0.14(random) +- 0.16(sys). This value agrees well with the distance estimates of four other galaxies in the M81 Group. In addition to the RGB stars, we observe a concentration of upper main sequence stars in the halo of NGC3077, which coincides partially with a feature known as the ``Garland''. Using Padua isochrones, these stars are estimated to be <150 Myrs old. Assuming that the nearest encounter between NGC3077 and M81 occurred 280 Myrs ago as predicted by the numerical simulations (Yun 1997), the observed upper main sequence stars are likely the results of the star formation triggered by the M81-NGC3077 tidal interaction.Comment: 15 pages, 8 figures. Accepted for publication in Astrophysical Journa

An Adaptive Optics Survey of Stellar Variability at the Galactic Center

We present a $\approx 11.5$ year adaptive optics (AO) study of stellar variability and search for eclipsing binaries in the central $\sim 0.4$ pc ($\sim 10''$) of the Milky Way nuclear star cluster. We measure the photometry of 563 stars using the Keck II NIRC2 imager ($K'$-band, $\lambda_0 = 2.124 \text{ } \mu \text{m}$). We achieve a photometric uncertainty floor of $\Delta m_{K'} \sim 0.03$ ($\approx 3\%$), comparable to the highest precision achieved in other AO studies. Approximately half of our sample ($50 \pm 2 \%$) shows variability. $52 \pm 5\%$ of known early-type young stars and $43 \pm 4 \%$ of known late-type giants are variable. These variability fractions are higher than those of other young, massive star populations or late-type giants in globular clusters, and can be largely explained by two factors. First, our experiment time baseline is sensitive to long-term intrinsic stellar variability. Second, the proper motion of stars behind spatial inhomogeneities in the foreground extinction screen can lead to variability. We recover the two known Galactic center eclipsing binary systems: IRS 16SW and S4-258 (E60). We constrain the Galactic center eclipsing binary fraction of known early-type stars to be at least $2.4 \pm 1.7\%$. We find no evidence of an eclipsing binary among the young S-stars nor among the young stellar disk members. These results are consistent with the local OB eclipsing binary fraction. We identify a new periodic variable, S2-36, with a 39.43 day period. Further observations are necessary to determine the nature of this source.Comment: 69 pages, 28 figures, 12 tables. Accepted for publication in The Astrophysical Journa

Anthropogenic nest material use in a global sample of birds

As humans increasingly modify the natural world, many animals have responded by changing their behaviour. Understanding and predicting the extent of these responses is a key step in conserving these species. For example, the tendency for some species of birds to incorporate anthropogenic items—particularly plastic material—into their nests is of increasing concern, as in some cases, this behaviour has harmful effects on adults, young and eggs. Studies of this phenomenon, however, have to date been largely limited in geographic and taxonomic scope. To investigate the global correlates of anthropogenic (including plastic) nest material use, we used Bayesian phylogenetic mixed models and a data set of recorded nest materials in 6147 species of birds. We find that, after controlling for research effort and proximity to human landscape modifications, anthropogenic nest material use is correlated with synanthropic (artificial) nesting locations, breeding environment and the number of different nest materials the species has been recorded to use. We also demonstrate that body mass, range size, conservation status and brain size do not explain variation in the recorded use of anthropogenic nest materials. These results indicate that anthropogenic materials are more likely to be included in nests when they are more readily available, as well as potentially by species that are more flexible in their nest material choice

Beak shape and nest material use in birds

This work was supported by a BBSRC Discovery Fellowship (grant no. BB/S01019X/1); the John Templeton Foundation (grant no. 60501); and the European Research Council (grant no. 788203).The evolution of behaviour can both influence, and be influenced by, morphology. Recent advances in methods and data availability have facilitated broad-scale investigations of physical form and behavioural function in many contexts, but the relationship between animal morphology and object manipulation-particularly objects used in construction-remains largely unknown. Here, we employ a new global database of nest materials used by 5924 species of birds together with phylogenetically informed random forest models to evaluate the link between beak shape and these nest-building materials. We find that beak morphology, together with species diet and access to materials, can predict nest-material use above chance and with high accuracy (68-97%). Much of this relationship, however, is driven by phylogenetic signal and sampling biases. We therefore conclude that while variation in nest material use is linked with that of beak shape across bird species, these correlations are modulated by the ecological context and evolutionary history of these species.Publisher PDFPeer reviewe

Morphological and molecular characterisation of Streptomyces spp. which suppress pathogenic fungi

Streptomyces species are aerobes and chemoorganotrophic bacteria. These microorganisms produce a wide range of industrially significant compounds, specifically antibiotics and anti fungal substances. The objective of this study was to characterise soil-borne Streptomyces isolates using morphological and molecular traits in order to identify them to species level, and leverage from their potential to suppress the growth of Aspergillus flavus , Fusarium oxysporum and Penicillium italicum . Twenty-seven soil-borne putative Streptomyces, which elicited comprehensive\ua0antimicrobial activity against Aspergillus flavus, Fusarium oxysporum and Penicillium italicum, in a previous study, were evaluated. On the basis of morphology, the bacteria resembled the genus Streptomyces. Initially, colonies phenotypically appeared to have a relatively smooth surface but as growth progressed the bacteria developed a weft of aerial mycelium granular, powdery or velvety in appearance. Bacteria produced a wide variety of pigments which in turn were responsible for the colour of the vegetative and aerial mycelia, colour ranged from white to cream or buff shades and yellow to orange or brown. Microscopic analyses and morphological characteristics generated sub-groups of the isolates and clustered them according to their similarities. One bacterial strain was randomly selected from each cluster and investigated using molecular characteristics. Partial 16S rDNAs from the selected representative isolates from each subgroup, were sequenced and phylogenetic analysis performed. The 16S\ua0rDNA\ua0sequences of the isolates indicated that they were related to\ua0 Streptomyces species: S. bungoensis , S. thermocarboxydus , S. corchorusii and S. lasaliensis, that are known secondary metabolite producers possessing antimicrobial activity against plant pathogens.Les esp\ue8ces de Streptomyces sont des bact\ue9ries a\ue9robies et chimio-organotrophes. Ces micro-organismes produisent une large gamme de compos\ue9s d\u2019importance industrielle, en particulier des antibiotiques et des substances antifongiques. L\u2019objectif de cette \ue9tude \ue9tait de caract\ue9riser les isolats de Streptomyces transmis par le sol \ue0 l\u2019aide de traits morphologiques et mol\ue9culaires afin de les identifier au niveau de l\u2019esp\ue8ce, et de tirer parti de leur potentiel \ue0 supprimer la croissance d\u2019 Aspergillus flavus , Fusarium oxysporum et Penicillium italicum . Vingt-sept Streptomyces putatifs transmis par le sol, qui ont suscit\ue9 une activit\ue9 antimicrobienne compl\ue8te contre Aspergillus flavus, Fusarium oxysporum et Penicillium italicum, dans une \ue9tude pr\ue9c\ue9dente, ont \ue9t\ue9 \ue9valu\ue9s. Sur la base de la morphologie, les bact\ue9ries ressemblaient au genre Streptomyces. Au d\ue9part, les colonies semblaient ph\ue9notypiquement avoir une surface relativement lisse, mais au fur et \ue0 mesure que la croissance progressait, les bact\ue9ries d\ue9veloppaient une trame de myc\ue9lium a\ue9rien d\u2019aspect granuleux, poudreux ou velout\ue9. Les bact\ue9ries produisaient une grande vari\ue9t\ue9 de pigments qui \ue0 leur tour \ue9taient responsables de la couleur des myc\ue9liums v\ue9g\ue9tatifs et a\ue9riens, la couleur variait du blanc au cr\ue8me ou au chamois et du jaune \ue0 l\u2019orange ou au brun. Des analyses microscopiques et des caract\ue9ristiques morphologiques ont g\ue9n\ue9r\ue9 des sous-groupes d\u2019isolats et les ont regroup\ue9s en fonction de leurs similitudes. Une souche bact\ue9rienne a \ue9t\ue9 s\ue9lectionn\ue9e au hasard dans chaque groupe et \ue9tudi\ue9e en utilisant des caract\ue9ristiques mol\ue9culaires. Des ADNr 16S partiels provenant des isolats repr\ue9sentatifs s\ue9lectionn\ue9s de chaque sous-groupe ont \ue9t\ue9 s\ue9quenc\ue9s et une analyse phylog\ue9n\ue9tique a \ue9t\ue9 effectu\ue9e. Les s\ue9quences d\u2019ADNr 16S des isolats ont indiqu\ue9 qu\u2019ils \ue9taient apparent\ue9s aux esp\ue8ces de Streptomyces: S. bungoensis , S. thermocarboxydus , S. corchorusii et S. lasaliensis, qui sont des producteurs de m\ue9tabolites secondaires connus poss\ue9dant une activit\ue9 antimicrobienne contre les phytopathog\ue8nes

In vitro suppression of pathogenic fungi by Streptomyces spp.

The use of living organisms or natural enemies of pathogens to control their populations is called biological disease control. It involves harnessing and introduction of exotic species of microorganism in a natural form, with the intention of controlling pathogens that may exist naturally in the same ecosystem. Prospects for biological control of Aspergillus flavus , Fusarium oxysporum and Penicillium italicum were investigated using Streptomyces spp. isolated from Chinhoyi University of Technology Farm soils in Mashonaland West, Zimbabwe. Twenty seven Streptomyces spp were obtained from the soil, and screened for antimicrobial activity and antagonism in in vitro pathogen inhibition assays, replicated thrice. Although majority of the isolates tested elicited no effect on test pathogens, 22% of the Streptomyces isolates were able to effectively suppress A. flavus, F. oxysporum and P. italicum by at least 55%. There was a significant interaction between Streptomyces isolates and pathogen (A. flavus, F. oxysporum and P. italicum) (P&lt;0.05) on fungal radial growth at days 7, 10 and 14 after pathogen-Streptomyces incubation. Antimicrobial potential against individual and multiple test pathogens was observed, with CUT-Streptomyces 4, CUT-Streptomyces 10, CUT-Streptomyces 11, CUT-Streptomyces 20 and CUT-Streptomyces 23 showing the greatest antimicrobial activity. CUT-Streptomyces isolates have the potential to suppress A. flavus, F. oxysporum and P. italicum in vitro.L\u2019utilisation d\u2019organismes vivants ou d\u2019ennemis naturels d\u2019agents pathog\ue8nes pour contr\uf4ler leurs populations est appel\ue9e contr\uf4le biologique des maladies. Il s\u2019agit d\u2019exploiter et d\u2019introduire des esp\ue8ces exotiques de microorganismes sous une forme naturelle, dans le but de contr\uf4ler les agents pathog\ue8nes pouvant exister naturellement dans le m\ueame \ue9cosyst\ue8me. Les perspectives de lutte biologique contre Aspergillus flavus , Fusarium oxysporum et Penicillium italicum ont \ue9t\ue9 \ue9tudi\ue9es \ue0 l\u2019aide de Streptomyces spp. isol\ue9es des sols agricoles de l\u2019Universit\ue9 de Technologie de Chinhoyi \ue0 Mashonaland West, Zimbabwe. Vingt-sept Streptomyces spp ont \ue9t\ue9 obtenus du sol et cribl\ue9s pour l\u2019activit\ue9 antimicrobienne et l\u2019antagonisme dans des tests d\u2019inhibition des agents pathog\ue8nes in vitro, r\ue9pliqu\ue9s trois fois. Bien que la majorit\ue9 des isolats test\ue9s ne provoquent aucun effet sur les agents pathog\ue8nes test\ue9s, 22% des isolats de Streptomyces sont capables de supprimer efficacement au moins 55% des A. flavus, F. oxysporum et P. italicum. Il y avait une interaction significative entre les isolats de Streptomyces et l\u2019agent pathog\ue8ne (A. flavus, F. oxysporum et P. italicum) (P&lt; 0.05) lors de la croissance radiale des champignons aux 7\ue8me, 10\ue8me et 14\ue8me jours apr\ue8s l\u2019incubation de l\u2019agent pathog\ue8ne-Streptomyces. Un potentiel antimicrobien contre des agents pathog\ue8nes individuels et multiples a \ue9t\ue9 observ\ue9. CUT-Streptomyces 4, CUT-Streptomyces 10, CUT-Streptomyces 11, CUT-Streptomyces 20 et CUT-Streptomyces 23 ont montr\ue9 l\u2019activit\ue9 antimicrobienne la plus \ue9lev\ue9e. Les isolats de CUT-Streptomyces ont le potentiel de supprimer A. flavus, F. oxysporum et P. italicum in vitro