1,288 research outputs found
Transmission spectra and valley processing of graphene and carbon nanotube superlattices with inter-valley coupling
published_or_final_versio
Vertical leakage mechanism in GaN on Si high electron mobility transistor buffer layers
Control of leakage currents in the buffer layers of GaN based transistors on Si substrates is vital for the demonstration of high performance devices. Here, we show that the growth conditions during the metal organic chemical vapour deposition growth of the graded AlGaN strain relief layers (SRLs) can significantly influence the vertical leakage. Using scanning capacitance microscopy, secondary ion mass spectrometry, and transmission electron microscopy, we investigate the origins of leakage paths and show that they result from the preferential incorporation of oxygen impurities on the side wall facets of the inverted hexagonal pyramidal pits which can occur during the growth of the graded AlGaN SRL. We also show that when 2D growth of the AlGaN SRL is maintained a significant increase in the breakdown voltage can be achieved even in much thinner buffer layer structures. These results demonstrate the importance of controlling the morphology of the high electron mobility transistor buffer layer as even at a very low density the leakage paths identified would provide leakage paths in large area devices.This work was funded by the Engineering and Physical Sciences Research Council under Grant Code Nos. EP/K014471/1 and EP/N01202X/1 and the European Research Council under the European Community's Seventh Framework Programme Grant Agreement No. 279361 (MACONS)
Quadrupole deformations of neutron-drip-line nuclei studied within the Skyrme Hartree-Fock-Bogolyubov approach
We introduce a local-scaling point transformation to allow for modifying the
asymptotic properties of the deformed three-dimensional Cartesian harmonic
oscillator wave functions. The resulting single-particle bases are very well
suited for solving the Hartree-Fock-Bogoliubov equations for deformed drip-line
nuclei. We then present results of self-consistent calculations performed for
the Mg isotopes and for light nuclei located near the two-neutron drip line.
The results suggest that for all even-even elements with =10--18 the most
weakly-bound nucleus has an oblate ground-state shape.Comment: 20 pages, 7 figure
The lncRNA HOTAIR transcription is controlled by HNF4α-induced chromatin topology modulation
The expression of the long noncoding RNA HOTAIR (HOX Transcript Antisense Intergenic RNA) is largely deregulated in epithelial cancers and positively correlates with poor prognosis and progression of hepatocellular carcinoma and gastrointestinal cancers. Furthermore, functional studies revealed a pivotal role for HOTAIR in the epithelial-to-mesenchymal transition, as this RNA is causal for the repressive activity of the master factor SNAIL on epithelial genes. Despite the proven oncogenic role of HOTAIR, its transcriptional regulation is still poorly understood. Here hepatocyte nuclear factor 4-α (HNF4α), as inducer of epithelial differentiation, was demonstrated to directly repress HOTAIR transcription in the mesenchymal-to epithelial transition. Mechanistically, HNF4α was found to cause the release of a chromatin loop on HOTAIR regulatory elements thus exerting an enhancer-blocking activity
Superconductivity induced by cobalt doping in iron-based oxyarsenides
Chemical doping has recently become a very important strategy to induce
superconductivity especially in complex compounds. Distinguished examples
include Ba-doped LaCuO (the first high temperature superconductor),
K-doped BaBiO, K-doped C and NaCoOHO. The
most recent example is F-doped LaFeAsO, which leads to a new class of high
temperature superconductors. One notes that all the above dopants are
non-magnetic, because magnetic atoms generally break superconducting Cooper
pairs. In addition, the doping site was out of the (super)conducting structural
unit (layer or framework). Here we report that superconductivity was realized
by doping magnetic element cobalt into the (super)conducting-active
FeAs layers in LaFeCoAsO. At surprisingly small Co-doping
level of =0.025, the antiferromagnetic spin-density-wave transition in the
parent compound is completely suppressed, and superconductivity with
10 K emerges. With increasing Co content, shows a maximum of 13 K at
, and then drops to below 2 K at =0.15. This result suggests
essential differences between previous cuprate superconductor and the present
iron-based arsenide one.Comment: 4 pages, 4 figure
Asymmetric triplex metallohelices with high and selective activity against cancer cells
Small cationic amphiphilic α-helical peptides are emerging as agents for the treatment of cancer and infection, but they are costly and display unfavourable pharmacokinetics. Helical coordination complexes may offer a three-dimensional scaffold for the synthesis of mimetic architectures. However, the high symmetry and modest functionality of current systems offer little scope to tailor the structure to interact with specific biomolecular targets, or to create libraries for phenotypic screens. Here, we report the highly stereoselective asymmetric self-assembly of very stable, functionalized metallohelices. Their anti-parallel head-to-head-to-tail ‘triplex’ strand arrangement creates an amphipathic functional topology akin to that of the active sub-units of, for example, host-defence peptides and p53. The metallohelices display high, structure-dependent toxicity to the human colon carcinoma cell-line HCT116 p53++, causing dramatic changes in the cell cycle without DNA damage. They have lower toxicity to human breast adenocarcinoma cells (MDA-MB-468) and, most remarkably, they show no significant toxicity to the bacteria methicillin-resistant Staphylococcus aureus and Escherichia coli.
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