843 research outputs found
Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction
We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.Comment: 4 pages, 2 figures; published versio
Oxidation states and magnetism of Fe nanoparticles prepared by a laser evaporation technique
Nanoparticles of iron and iron oxide have been prepared in a thermal diffusion cloud chamber using pulsed laser evaporation. SEM/TEM studies of these particles reveal a size distribution with a mean diameter of about 60 Ă
. This is consistent with the mean particle size estimated from the magnetic data. The oxidation levels of these nanoparticles prepared at different partial oxygen pressures were investigated using FTIR. All the samples are found to exhibit superparamagnetism with blocking temperatures ranging from 50 K to above room temperature. Magnetic anisotropy constants are calculated from the frequency dependence of the blocking temperatures are found to be one quarter of magnitude higher than is known for the bulk
Sputtering of polished EUROFER97 steel: Surface structure modification and enrichment with tungsten and tantalum
Electrical control of the Kondo effect in a helical edge liquid
Magnetic impurities affect the transport properties of the helical edge
states of quantum spin Hall insulators by causing single-electron
backscattering. We study such a system in the presence of a Rashba spin-orbit
interaction induced by an external electric field, showing that this can be
used to control the Kondo temperature, as well as the correction to the
conductance due to the impurity. Surprisingly, for a strongly anisotropic
electron-impurity spin exchange, Kondo screening may get obstructed by the
presence of a non-collinear spin interaction mediated by the Rashba coupling.
This challenges the expectation that the Kondo effect is stable against
time-reversal invariant perturbations.Comment: 7 pages, 2 figures. Expression for the current operator corrected.
(Conclusions unaffected.) Erratum to be publishe
Long-term in situ observations of biomass burning aerosol at a high altitude station in Venezuela : sources, impacts and interannual variability
Long-term in situ observations of biomass burning aerosol at a high altitude station in Venezuela â sources, impacts and interannual variability
First long-term observations of South American biomass burning aerosol within the tropical lower free troposphere are presented. The observations were conducted between 2007 and 2009 at a high altitude station (4765 m a.s.l.) on the Pico Espejo, Venezuela. Sub-micron aerosol volume, number concentrations of primary particles and particle absorption were observed. Orographic lifting and shallow convection leads to a distinct diurnal cycle at the station. It enables measurements within the lower free troposphere during night time and observations of boundary layer air masses during day time and at their transitional regions. The seasonal cycle is defined by a wet rainy season and a dry biomass burning season. The particle load of biomass burning aerosol is dominated by fires in the Venezuelan savannah. Increases of aerosol concentrations could not be linked to long-range transport of biomass burning plumes from the Amazon basin or Africa due to effective wet scavenging of particles. Highest particle concentrations were observed within boundary layer air masses during the dry season. Ambient sub-micron aerosol volume reached 1.4 ± 1.3 μm<sup>3</sup> cm<sup>−3</sup>, heated (300 °C) particle number concentrations 510 ± 420 cm<sup>−3</sup> and the absorption coefficient 0.91 ± 1.2 Mm<sup>−1</sup>. The respective concentrations were lowest within the lower free troposphere during the wet season and averaged at 0.19 ± 0.25 μm<sup>3</sup> cm<sup>−3</sup>, 150 ± 94 cm<sup>−3</sup> and 0.15 ± 0.26 Mm<sup>−1</sup>. A decrease of particle concentrations during the dry seasons from 2007â2009 could be connected to a decrease in fire activity in the wider region of Venezuela using MODIS satellite observations. The variability of biomass burning is most likely linked to the El Niño-Southern Oscillation (ENSO). Low biomass burning activity in the Venezuelan savannah was observed to follow La Niña conditions, high biomass burning activity followed El Niño conditions
Cosmic multi-muon events observed in the underground CERN-LEP tunnel with the ALEPH experiment
Multimuon events have been recorded with the ALEPH-detector, located 140 m underground, in parallel with ee data taking. Benefitting from the high spatial and momentum resolution of the ALEPH tracking chambers narrowly spaced muons in high multiplicity bundles could be analysed. The bulk of the data can be successfully described by standard production phenomena. The multiplicity distribution favors, though not with very high significance, a chemical composition which changes from light to heavier elements with increasing energy around the ``knee". The five highest multiplicity events, with up to 150 muons within an area of 8 m, occur with a frequency which is almost an order of magnitude above the simulation. To establish a possible effect, more of these events should be recorded with a larger area detector
Nitrate dry deposition in Svalbard
This is the final version of the article. Available from Taylor & Francis via the DOI in this record.Arctic regions are generally nutrient limited, receiving an extensive part of their bio-available nitrogen from the deposition of atmospheric reactive nitrogen. Reactive nitrogen oxides, as nitric acid (HNO3) and nitrate aerosols (p-NO3), can either be washed out from the atmosphere by precipitation or dry deposited, dissolving to nitrate (). During winter, is accumulated in the snowpack and released as a pulse during spring melt. Quantification of deposition is essential to assess impacts on Arctic terrestrial ecology and for ice core interpretations. However, the individual importance of wet and dry deposition is poorly quantified in the high Arctic regions where in-situ measurements are demanding. In this study, three different methods are employed to quantify dry deposition around the atmospheric and ecosystem monitoring site, Ny-Ă
lesund, Svalbard, for the winter season (September 2009 to May 2010): (1) A snow tray sampling approach indicates a dry deposition of â10.27±3.84 mg mâ2 (± S.E.); (2) A glacial sampling approach yielded somewhat higher values â30.68±12.00 mg mâ2; and (3) Dry deposition was also modelled for HNO3 and p-NO3 using atmospheric concentrations and stability observations, resulting in a total combined nitrate dry deposition of â10.76±1.26 mg mâ2. The model indicates that deposition primarily occurs via HNO3 with only a minor contribution by p-NO3. Modelled median deposition velocities largely explain this difference: 0.63 cm sâ1 for HNO3 while p-NO3 was 0.0025 and 0.16 cm sâ1 for particle sizes 0.7 and 7 ”m, respectively. Overall, the three methods are within two standard errors agreement, attributing an average 14% (total range of 2â44%) of the total nitrate deposition to dry deposition. Dry deposition events were identified in association with elevated atmospheric concentrations, corroborating recent studies that identified episodes of rapid pollution transport and deposition to the Arctic.As a part of the international project âSources, sinks and impacts of atmospheric nitrogen deposition in the Arcticâ (NSINK), this project received financial support from an EU Marie Curie Initial Stage Training Network Award NSINK (FP7 215503) and fieldwork were supported by an Arctic Field Grant, Svalbard Science Forum. NILU's atmospheric monitoring program at the Zeppelin Station is financed by the Norwegian Climate and Pollution Agency and ITM's research at the same station is supported by the Swedish Environmental Protection Agency. This is also a contribution to âCrysophere-Atmosphere interaction in a changing Arctic climate (CRAICC)â a Top-Level Research Initiative (TRI). Logistic support was provided by the Norwegian Polar Institute staff at the Sverdrup Station, Ny-Ă
lesund, while A. Nowak-Zwierz, K. A. Kozio and C. L. Chakrabarti contributed to the analytical work in Sheffield, and J. Kohler kindly provided snow accumulation data from Austre BrĂžggerbreen
MTH1 inhibitor TH588 induces mitosis-dependent accumulation of genomic 8-oxodG and disturbs mitotic progression
Reactive oxygen species (ROS) oxidise nucleotide triphosphate pools (e.g., 8-oxodGTP), which may kill cells if incorporated into DNA. Whether cancers avoid poisoning from oxidised nucleotides by preventing incorporation via the oxidised purine diphosphatase MTH1 remains under debate. Also, little is known about DNA polymerases incorporating oxidised nucleotides in cells or how oxidised nucleotides in DNA become toxic. We show replacement of one of the main DNA replicases in human cells, DNA polymerase delta (Pol ÎŽ), to an error-prone variant allows increased 8-oxodG accumulation into DNA following treatment with the MTH1 inhibitor (MTH1i) TH588. The resulting elevated genomic 8-oxodG correlates with increased cytotoxicity of TH588. Interestingly, no substantial perturbation of replication fork progression is observed, but rather mitotic progression is impaired and mitotic DNA synthesis triggered. Reducing mitotic arrest by reversin treatment prevents accumulation of genomic 8-oxodG and reduces cytotoxicity of TH588, in line with the notion that mitotic arrest is required for ROS build-up and oxidation of the nucleotide pool. Furthermore, we demonstrate delayed mitosis and increased mitotic cell death following TH588 treatment in cells expressing the error-prone Pol ÎŽ variant, which is not observed following treatments with anti-mitotic agents, thus linking incorporation of oxidised nucleotides and disturbed mitotic progression
Correlated local distortions of the TlO layers in TlBaCuO: An x-ray absorption study
We have used the XAFS (x-ray-absorption fine structure) technique to
investigate the local structure about the Cu, Ba, and Tl atoms in orthorhombic
Tl-2201 with a superconducting transition temperature T=60 K. Our results
clearly show that the O(1), O(2), Cu, and Ba atoms are at their ideal sites as
given by the diffraction measurements, while the Tl and O(3) atoms are more
disordered than suggested by the average crystal structure. The Tl-Tl distance
at 3.5 \AA{ } between the TlO layers does not change, but the Tl-Tl distance at
3.9 \AA{ } within the TlO layer is not observed and the Tl-Ba and Ba-Tl peaks
are very broad. The shorter Tl-O(3) distance in the TlO layer is about 2.33
\AA, significantly shorter than the distance calculated with both the Tl and
O(3) atoms at their ideal sites ( 0 or ). A model based
on these results shows that the Tl atom is displaced along the
directions from its ideal site by about 0.11 \AA; the displacements of
neighboring Tl atoms are correlated. The O(3) atom is shifted from the $4e$
site by about 0.53 \AA{ } roughly along the directions. A comparison of
the Tl L-edge XAFS spectra from three samples, with T=60 K, 76 K,
and 89 K, shows that the O environment around the Tl atom is sensitive to T
while the Tl local displacement is insensitive to T and the structural
symmetry. These conclusions are compared with other experimental results and
the implications for charge transfer and superconductivity are discussed. This
paper has been submitted to Phys. Rev. B.Comment: 20 pages plus 14 ps figures, REVTEX 3.
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