428 research outputs found
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 CeO and
CeO. 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
CeO, the excess charge resulting from removal of an oxygen atom
delocalizes among all three triclinic Ce sites closest to the O vacancy. In
CeO, 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 PrO, we also
predict that the charge in CeO 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 year adaptive optics (AO) study of stellar
variability and search for eclipsing binaries in the central pc
() of the Milky Way nuclear star cluster. We measure the photometry
of 563 stars using the Keck II NIRC2 imager (-band, ). We achieve a photometric uncertainty floor of (), comparable to the highest precision achieved
in other AO studies. Approximately half of our sample () shows
variability. of known early-type young stars and 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 . 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
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.This article is part of the theme issue ‘The evolutionary ecology of nests: a cross-taxon approach’
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<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< 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
- …