12 research outputs found
TiO2 anatase with a bandgap in the visible region.
TiO2 anatase plays a central role in energy and environmental research. A major bottleneck toward developing artificial photosynthesis with TiO2 is that it only absorbs ultraviolet light, owing to its large bandgap of 3.2 eV. If one could reduce the bandgap of anatase to the visible region, TiO2-based photocatalysis could become a competitive clean energy source. Here, using scanning tunneling microscopy and spectroscopy in conjunction with density functional theory calculations, we report the discovery of a highly reactive titanium-terminated anatase surface with a reduced bandgap of less than 2 eV, stretching into the red portion of the solar spectrum. By tuning the surface preparation conditions, we can reversibly switch between the standard anatase surface and the newly discovered low bandgap surface phase. The identification of a TiO2 anatase surface phase with a bandgap in the visible and high chemical reactivity has important implications for solar energy conversion, photocatalysis, and artificial photosynthesis
Genomic survey of pathogenicity determinants and VNTR markers in the cassava bacterial pathogen <em>Xanthomonas axonopodis</em> pv. <em>manihotis</em> strain CIO151
Xanthomonas axonopodis pv. manihotis (Xam) is the causal agent of bacterial blight of cassava, which is among the main components of human diet in Africa and South America. Current information about the molecular pathogenicity factors involved in the infection process of this organism is limited. Previous studies in other bacteria in this genus suggest that advanced draft genome sequences are valuable resources for molecular studies on their interaction with plants and could provide valuable tools for diagnostics and detection. Here we have generated the first manually annotated high-quality draft genome sequence of Xam strain CIO151. Its genomic structure is similar to that of other xanthomonads, especially Xanthomonas euvesicatoria and Xanthomonas citri pv. citri species. Several putative pathogenicity factors were identified, including type III effectors, cell wall-degrading enzymes and clusters encoding protein secretion systems. Specific characteristics in this genome include changes in the xanthomonadin cluster that could explain the lack of typical yellow color in all strains of this pathovar and the presence of 50 regions in the genome with atypical nucleotide composition. The genome sequence was used to predict and evaluate 22 variable number of tandem repeat (VNTR) loci that were subsequently demonstrated as polymorphic in representative Xam strains. Our results demonstrate that Xanthomonas axonopodis pv. manihotis strain CIO151 possesses ten clusters of pathogenicity factors conserved within the genus Xanthomonas. We report 126 genes that are potentially unique to Xam, as well as potential horizontal transfer events in the history of the genome. The relation of these regions with virulence and pathogenicity could explain several aspects of the biology of this pathogen, including its ability to colonize both vascular and non-vascular tissues of cassava plants. A set of 16 robust, polymorphic VNTR loci will be useful to develop a multi-locus VNTR analysis scheme for epidemiological surveillance of this disease. (Résumé d'auteur
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Doping liquid argon with xenon in ProtoDUNE Single-Phase: effects on scintillation light
Abstract
Doping of liquid argon TPCs (LArTPCs) with a small
concentration of xenon is a technique for light-shifting and
facilitates the detection of the liquid argon scintillation
light. In this paper, we present the results of the first doping
test ever performed in a kiloton-scale LArTPC. From February to May
2020, we carried out this special run in the single-phase DUNE Far
Detector prototype (ProtoDUNE-SP) at CERN, featuring 720 t of total
liquid argon mass with 410 t of fiducial mass. A 5.4 ppm nitrogen
contamination was present during the xenon doping campaign. The goal
of the run was to measure the light and charge response of the
detector to the addition of xenon, up to a concentration of
18.8 ppm. The main purpose was to test the possibility for
reduction of non-uniformities in light collection, caused by
deployment of photon detectors only within the anode planes. Light
collection was analysed as a function of the xenon concentration, by
using the pre-existing photon detection system (PDS) of ProtoDUNE-SP
and an additional smaller set-up installed specifically for this
run. In this paper we first summarize our current understanding of
the argon-xenon energy transfer process and the impact of the
presence of nitrogen in argon with and without xenon dopant. We then
describe the key elements of ProtoDUNE-SP and the injection method
deployed. Two dedicated photon detectors were able to collect the
light produced by xenon and the total light. The ratio of these
components was measured to be about 0.65 as 18.8 ppm of xenon were
injected. We performed studies of the collection efficiency as a
function of the distance between tracks and light detectors,
demonstrating enhanced uniformity of response for the anode-mounted
PDS. We also show that xenon doping can substantially recover light
losses due to contamination of the liquid argon by nitrogen.</jats:p