Erratum: “Seed layer technique for high quality epitaxial manganite films” [AIP Advances 6, 085109 (2016)]

No abstract available

Protein-DNA charge transport: Redox activation of a DNA repair protein by guanine radical

DNA charge transport (CT) chemistry provides a route to carry out oxidative DNA damage from a distance in a reaction that is sensitive to DNA mismatches and lesions. Here, DNA-mediated CT also leads to oxidation of a DNA-bound base excision repair enzyme, MutY. DNA-bound Ru(III), generated through a flash/quench technique, is found to promote oxidation of the [4Fe-4S](2+) cluster of MutY to [4Fe-4S](3+) and its decomposition product [3Fe-4S](1+). Flash/quench experiments monitored by EPR spectroscopy reveal spectra with g = 2.08, 2.06, and 2.02, characteristic of the oxidized clusters. Transient absorption spectra of poly(dGC) and [Ru(phen)(2)dppz](3+) (dppz = dipyridophenazine), generated in situ, show an absorption characteristic of the guanine radical that is depleted in the presence of MutY with formation instead of a long-lived species with an absorption at 405 nm; we attribute this absorption also to formation of the oxidized [4Fe-4S](3+) and [3Fe4S](1+) clusters. In ruthenium-tethered DNA assemblies, oxidative damage to the 5'-G of a 5'-GG-3' doublet is generated from a distance but this irreversible damage is inhibited by MutY and instead EPR experiments reveal cluster oxidation. With ruthenium-tethered assemblies containing duplex versus single-stranded regions, MutY oxidation is found to be mediated by the DNA duplex, with guanine radical as an intermediate oxidant; guanine radical formation facilitates MutY oxidation. A model is proposed for the redox activation of DNA repair proteins through DNA CT, with guanine radicals, the first product under oxidative stress, in oxidizing the DNA-bound repair proteins, providing the signal to stimulate DNA repair

Optical bistability in Er-Yb co-doped phosphate glass microspheres at room temperature

We experimentally demonstrate optical bistability in Er3+-Yb3+ phosphate glass microspheres at 295 K. Bistability is associated with both Er3+ fluorescence and lasing behavior, and chromatic switching. The chromatic switching results from an intrinsic mechanism exploiting the thermal coupling of closely-spaced energy levels, and occurs simultaneously with the intensity switching. A contrast ratio of 3.2 has been obtained for chromatic switching, and the intensity switching shows ratios of 2.4 for 550 nm and, 1.8 for the 660 nm fluorescence emissions, and 11 for the IR lasing at 1.5 um. Concurrent with these observations, we investigate a temperature dependent absorption of pump power which exhibits bistable behavior. The influences of the host matrix on lasing and fluorescence mechanisms are highlighted.Comment: 22 pages, 6 figure

The application of a Trous wave filtering and Monte Carlo analysis on SECIS 2001 solar eclipse observations

8000 images of the Solar corona were captured during the June 2001 total Solar eclipse. New software for the alignment of the images and an automated technique for detecting intensity oscillations using multi scale wavelet analysis were developed. Large areas of the images covered by the Moon and the upper corona were scanned for oscillations and the statistical properties of the atmospheric effects were determined. The a Trous wavelet transform was used for noise reduction and Monte Carlo analysis as a significance test of the detections. The effectiveness of those techniques is discussed in detail.Comment: 17 pages, 8 figures, accepted by Solar Physics Journal for publication in Topical Issue: "Frontiers in Solar Image Processing

Designing a fully compensated half-metallic ferrimagnet

Recent experimental work on Mn2RuxGa demonstrates its potential as a compensated ferrimagnetic half-metal (CFHM). Here we present a set of high-throughput ab initio density functional theory calculations and detailed experimental characterisation, that enable us to correctly describe the nominal Mn2RuxGa thin films, in particular with regard to site-disorder and defects. We then construct models that accurately capture all the key features of the Mn-Ru-Ga system, including magnetic compensation and the spin gap at the Fermi level. We find that electronic doping is neccessary, which is achieved with a Mn/Ga ratio smaller than two. Our study shows how composition and substrate-induced biaxial strain can be combined to design a ferrimagnetic half-metal with a compensation point close to room temperature

The potency of the broad spectrum bacteriocin, bactofencin A, against staphylococci is highly dependent on primary structure, N-terminal charge and disulphide formation

Bactofencin A is a novel class IId bacteriocin, produced by the intestinal isolate Lactobacillus salivarius DPC6502, which has potent activity against medically significant pathogens including Staphylococcus aureus. This bacteriocin is unusual in that it has a highly cationic N terminus and a single disulfide bond between Cys7 and Cys22, resulting in a large C terminal loop. In this study, a library of synthetic bactofencin A variants were screened against the mastitis isolate, S. aureus DPC5246, to identify key residues responsible for activity. It was apparent that substituting either cysteine of the disulfide bond with either serine or alanine significantly reduced the activity of the bacteriocin, confirming the importance of the C terminal loop. Substituting N terminal amino acids with alanine had no effect on activity, whereas sequential removal of the N terminal positively charged residues resulted in an increasingly inactive peptide. A complete (synthetic) alanine scanning analysis revealed that the residues between Val9 and Gly17 were most affected by substitution suggesting that this area has a major influence on the potency of the bacteriocin. Substituting residues in the loop region between Cys7 and Cys22 for D-amino acid equivalents had a more detrimental effect on activity than L-alanine substitutions. Specifically Y10A, N11A, P15A and T16A are active at 4, 16, 1 and 16 μM respectively while their D equivalents were inactive at 1000 μM, the highest concentration tested. Ultimately, this study identifies the critical features in the primary structure of the bacteriocin which gives it such potent activity against pathogenic staphylococci

On the statistical detection of propagating waves in polar coronal holes

Waves are important for the heating of the solar corona and the acceleration of the solar wind. We have examined a long spectral time series of a northern coronal hole observed on the 20th October 1996, with the SUMER spectrometer onboard SoHO. The observations were obtained in a transition region N IV 765 A line and in a low coronal Ne VIII 770 A line. Our observations indicate the presence of compressional waves with periods of ~25 min. Using Fourier techniques, we measured the phase delays between intensity as well as velocity oscillations in the two chosen lines. From this we are able to measure the travel time of the propagating oscillations and, hence, the propagation speeds of the waves producing the oscillations. We found that there is a difference in the nature of the propagation in bright ('network') and dark ('internetwork') regions with the latter sometimes showing evidence for downwardly propagating waves that is not seen in the former. As, in all cases, the measured propagation speeds are subsonic, we concluded that the detected waves are slow magnetoacoustic in nature.Comment: 7 pages, 7 figure