1,928 research outputs found
Defect Tolerant Monolayer Transition Metal Dichalcogenides
Localized electronic states formed inside the band gap of a semiconductor due
to crystal defects can be detrimental to the material's optoelectronic
properties. Semiconductors with lower tendency to form defect induced deep gap
states are termed defect tolerant. Here we provide a systematic first
principles investigation of defect tolerance in 29 monolayer transition metal
dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that
the TMDs based on group VI and X metals form deep gap states upon creation of a
chalcogen (S, Se, Te) vacancy while the TMDs based on group IV metals form only
shallow defect levels and are thus predicted to be defect tolerant.
Interestingly, all the defect sensitive TMDs have valence and conduction bands
with very similar orbital composition. This indicates a bonding/anti-bonding
nature of the gap which in turn suggests that dangling bonds will fall inside
the gap. These ideas are made quantitative by introducing a descriptor that
measures the degree of similarity of the conduction and valence band manifolds.
Finally, the study is generalized to non-polar nanoribbons of the TMDs where we
find that only the defect sensitive materials form edge states within the band
gap
Linear and nonlinear frequency-domain modelling of oscillatory flow over submerged canopies
Acknowledgement ON acknowledges funding from the University of Aberdeen to support his PhD. The authors ac knowledge the support of the University of Aberdeen technical staff for the experimental work, especially that of Fluids Laboratory Technician Roy Gillanders. The experimental dataset is avail626 able on https://dx.doi.org/10.5281/zenodo.4560141 (will be released upon acceptance of the manuscript).Peer reviewedPublisher PD
Asymmetries in the perception of synthesized speech
It was previously observed [1] that the order of presentation of paired stimuli influenced the number of different responses in same-different tasks in speech synthesis evaluation. This paper investigates this phenomenon within the context of cognitive psychology and demonstrates that, as the cognitive psychology literature suggests, there is an effect relating to the prototypicality of the stimulus. Index Terms: speech synthesis, evaluation, perception, Blizzard Challeng
Machine Learning with bond information for local structure optimizations in surface science
Local optimization of adsorption systems inherently involves different
scales: within the substrate, within the molecule, and between molecule and
substrate. In this work, we show how the explicit modeling of the different
character of the bonds in these systems improves the performance of machine
learning methods for optimization. We introduce an anisotropic kernel in the
Gaussian process regression framework that guides the search for the local
minimum, and we show its overall good performance across different types of
atomic systems. The method shows a speed-up of up to a factor two compared with
the fastest standard optimization methods on adsorption systems. Additionally,
we show that a limited memory approach is not only beneficial in terms of
overall computational resources, but can result in a further reduction of
energy and force calculations
Accounting for imperfect forward modeling in geophysical inverse problems â Exemplified for crosshole tomography
PPE51 mediates uptake of trehalose across the mycomembrane of Mycobacterium tuberculosis
The disaccharide trehalose is essential for viability of Mycobacterium tuberculosis, which synthesizes trehalose de novo but can also utilize exogenous trehalose. The mycobacterial cell wall encompasses two permeability barriers, the cytoplasmic membrane and the outer mycolic acid-containing mycomembrane. The ABC transporter LpqY-SugA-SugB-SugC has previously been demonstrated to mediate the specific uptake of trehalose across the cytoplasmic membrane. However, it is still unclear how the transport of trehalose molecules across the mycomembrane is mediated. In this study, we harnessed the antimycobacterial activity of the analogue 6-azido trehalose to select for spontaneous resistant M. tuberculosis mutants in a merodiploid strain harbouring two LpqY-SugA-SugB-SugC copies. Mutations mediating resistance to 6-azido trehalose mapped to the proline-proline-glutamate (PPE) family member PPE51 (Rv3136), which has recently been shown to be an integral mycomembrane protein involved in uptake of low-molecular weight compounds. A site-specific ppe51 gene deletion mutant of M. tuberculosis was unable to grow on trehalose as the sole carbon source. Furthermore, bioorthogonal labelling of the M. tuberculosis Îppe51 mutant incubated with 6-azido trehalose corroborated the impaired internalization. Taken together, the results indicate that the transport of trehalose and trehalose analogues across the mycomembrane of M. tuberculosis is exclusively mediated by PPE51
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