119 research outputs found
Electron Correlation Effects in Resonant Inelastic X-ray Scattering of NaV2O5
Element- and site-specific resonant inelastic x-ray scattering spectroscopy
(RIXS) is employed to investigate electron correlation effects in {}. In contrast to single photon techniques, RIXS at the vanadium
edge is able to probe transitions between V d-bands. A sharp energy
loss feature is observed at -1.56 eV, which is well reproduced by a model
calculation including correlation effects. The calculation identifies the loss
feature as excitation between the lower and upper Hubbard bands and permits an
accurate determination of the Hubbard interaction term eV.Comment: 15 pages, four figures, accepted to Phys. Rev. Let
Soft x-ray spectroscopy measurements of the p-like density of states of B in MgB2 and evidence for surface boron oxides on exposed surfaces
Soft X-ray absorption and fluorescence measurements are reported for the
K-edge of B in MgB2. The measurements confirm a high density of B
pxy(sigma)-states at the Fermi edge and extending to approximately 0.9 eV above
the edge. A strong resonance is observed in elastic scattering through a
core-exciton derived from out-of-plane pz(pi*)-states. Another strong
resonance, observed in both elastic and inelastic spectra, is identified as a
product of surface boron oxides.Comment: 7 pages total, 4 figures, submitted to Phys. Rev. Let
Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots
Current steps attributed to resonant tunneling through individual InAs
quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated
experimentally in magnetic fields up to 28 T. The steps evolve into strongly
enhanced current peaks in high fields. This can be understood as a
field-induced Fermi-edge singularity due to the Coulomb interaction between the
tunneling electron on the quantum dot and the partly spin polarized Fermi sea
in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure
Electronic structure of MgB: X-ray emission and absorption studies
Measurements of x-ray emission and absorption spectra of the constituents of
MgB are presented. The results obtained are in good agreement with
calculated x-ray spectra, with dipole matrix elements taken into account. The
comparison of x-ray emission spectra of graphite, AlB, and MgB in the
binding energy scale supports the idea of charge transfer from to
bands, which creates holes at the top of the bonding bands and
drives the high-TComment: final version as published in PR
Electronic Structure of B-2p State in AlB2 Single Crystal: Direct Observation ofp\sigma and p\pi Density of States
X-ray emission (XES) and absorption (XAS) spectra near the B- edge were
measured on single-crystalline AlB compound which is an isostructural
diboride of superconducting MgB. The partial density of states (PDOS) of
B-2 and orbitals were derived from the polarization dependence
of XES and XAS spectra. There are considerable amounts of PDOS near the Fermi
energy in AlB similarly to that in MgB, but there are almost no PDOS in
orbitals of AlB near the Fermi energy, i.e., a pseudo-gap in
state and a broad metallic state in state are observed. The
present result indirectly supports scenarios that the holes play an
important role in the occurrence of superconductivity in MgB. The overall
features of PDOS were found to be in good agreement with the result of band
calculation of AlB, but a small discrepancy in the Fermi energy is
observed, which is attributed to the Al vacancy in the compounds, i.e., the
estimated concentration is AlB.Comment: LaTeX files and 4 eps figures, to be published in J. Phys. Soc. Jp
Orbital Symmetry of Ba(Fe1-xCox)2As2 Superconductors Probed with X-ray Absorption Spectroscopy
The orbital symmetries of electron doped iron-arsenide superconductors
Ba(Fe1-xCox)2As2 have been measured with x-ray absorption spectroscopy. The
data reveal signatures of Fe d electron itinerancy, weak electronic
correlations, and a high degree of Fe-As hybridization related to the bonding
topology of the Fe dxz+yz states, which are found to contribute substantially
at the Fermi level. The energies and detailed orbital character of Fe and As
derived unoccupied s and d states are found to be in remarkably good agreement
with the predictions of standard density functional theory.Comment: Accepted for publication in Phys. Rev. B, 3 figures. Minor
corrections adde
Axial Globe Position Measurement: A Prospective Multicenter Study by the International Thyroid Eye Disease Society
Identify a reproducible measure of axial globe position (AGP) for multicenter studies on patients with thyroid eye disease (TED)
Distributional Patterns of Pseudacteon Associated with the Solenopsis saevissima Complex in South America
Classical biological control efforts against imported fire ants have largely involved the use of Pseudacteon parasitoids. To facilitate further exploration for species and population biotypes a database of collection records for Pseudacteon species was organized, including those from the literature and other sources. These data were then used to map the geographical ranges of species associated with the imported fire ants in their native range in South America. In addition, we found geographical range metrics for all species in the genus and related these metrics to latitude and host use. Approximately equal numbers of Pseudacteon species were found in temperate and tropical regions, though the majority of taxa found only in temperate areas were found in the Northern Hemisphere. No significant differences in sizes of geographical ranges were found between Pseudacteon associated with the different host complexes of fire ants despite the much larger and systemic collection effort associated with the S. saevissima host group. The geographical range of the flies was loosely associated with both the number of hosts and the geographical range of their hosts. Pseudacteon with the most extensive ranges had either multiple hosts or hosts with broad distributions. Mean species richnesses of Pseudacteon in locality species assemblages associated with S. saevissima complex ants was 2.8 species, but intensively sampled locations were usually much higher. Possible factors are discussed related to variation in the size of geographical range, and areas in southern South America are outlined that are likely to have been under-explored for Pseudacteon associated with imported fire ants
Pyrokinin β-Neuropeptide Affects Necrophoretic Behavior in Fire Ants (S. invicta), and Expression of β-NP in a Mycoinsecticide Increases Its Virulence
Fire ants are one of the world's most damaging invasive pests, with few means for their effective control. Although ecologically friendly alternatives to chemical pesticides such as the insecticidal fungus Beauveria bassiana have been suggested for the control of fire ant populations, their use has been limited due to the low virulence of the fungus and the length of time it takes to kill its target. We present a means of increasing the virulence of the fungal agent by expressing a fire ant neuropeptide. Expression of the fire ant (Solenopsis invicta) pyrokinin β -neuropeptide (β-NP) by B. bassiana increased fungal virulence six-fold towards fire ants, decreased the LT50, but did not affect virulence towards the lepidopteran, Galleria mellonella. Intriguingly, ants killed by the β-NP expressing fungus were disrupted in the removal of dead colony members, i.e. necrophoretic behavior. Furthermore, synthetic C-terminal amidated β-NP but not the non-amidated peptide had a dramatic effect on necrophoretic behavior. These data link chemical sensing of a specific peptide to a complex social behavior. Our results also confirm a new approach to insect control in which expression of host molecules in an insect pathogen can by exploited for target specific augmentation of virulence. The minimization of the development of potential insect resistance by our approach is discussed
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