20 research outputs found
Monodomain to polydomain transition in ferroelectric PbTiO3 thin films with La0.67Sr0.3MnO3 electrodes
Finite size effects in ferroelectric thin films have been probed in a series
of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin
La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down
to 28 A (7 unit cells). The evolution of the film tetragonality c/a, studied
using high resolution x-ray diffraction measurements, shows first a decrease of
c/a with decreasing film thickness followed by a recovery of c/a at small
thicknesses. This recovery is accompanied by a change from a monodomain to a
polydomain configuration of the polarization, as directly demonstrated by
piezoresponse atomic force microscopy measurements
Fermi surface induced lattice distortion in NbTe
The origin of the monoclinic distortion and domain formation in the quasi
two-dimensional layer compound NbTe is investigated. Angle-resolved
photoemission shows that the Fermi surface is pseudogapped over large portions
of the Brillouin zone. Ab initio calculation of the electron and phonon
bandstructure as well as the static RPA susceptibility lead us to conclude that
Fermi surface nesting and electron-phonon coupling play a key role in the
lowering of the crystal symmetry and in the formation of the charge density
wave phase
Increasing Trends of Association of 16S rRNA Methylases and Carbapenemases in Enterobacterales Clinical Isolates from Switzerland, 2017–2020
Aminoglycosides (AGs) in combination with β-lactams play an important role in antimicrobial therapy in severe infections. Pan-resistance to clinically relevant AGs increasingly arises from the production of 16S rRNA methylases (RMTases) that are mostly encoded by plasmids in Gram-negative bacteria. The recent emergence and spread of isolates encoding RMTases is worrisome, considering that they often co-produce extended-spectrum β-lactamases (ESBLs) or carbapenemases. Our study aimed to retrospectively analyze and characterize the association of carbapenem- and aminoglycoside-resistant clinical isolates in Switzerland during a 3.5-year period between January 2017 and June 2020. A total of 103 pan-aminoglycoside- and carbapenem-resistant clinical isolates were recovered at the NARA (Swiss National Reference Center for Emerging Antibiotic Resistance) during the 2017–2020 period. Carbapenemase and RMTase determinants were identified by PCR and sequencing. The characterization of plasmids bearing resistance determinants was performed by a mating-out assay followed by PCR-based replicon typing (PBRT). Clonality of the isolates was investigated by multilocus sequence typing (MLST). Over the 991 Enterobacterales collected at the NARA during this period, 103 (10.4%) of them were resistant to both carbapenems and all aminoglycosides. Among these 103 isolates, 35 isolates produced NDM-like carbapenemases, followed by OXA-48-like (n = 23), KPC-like (n = 21), or no carbapenemase (n = 13), OXA-48-like and NDM-like co-production (n = 7), and VIM-like enzymes (n = 4). The RMTases ArmA, RmtB, RmtC, RmtF, RmtG, and RmtB + RmtF were identified among 51.4%, 13.6%, 4.9%, 24.3%, 1%, and 1%, respectively. Plasmid co-localization of the carbapenemase and the RMTase encoding genes was found among ca. 20% of the isolates. A high diversity was identified in terms of the nature of associations between RMTase and carbapenemase-encoding genes, of incompatibility groups of the corresponding plasmids, and of strain genetic backgrounds, highlighting heterogeneous importations rather than clonal dissemination