2,072 research outputs found
Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO
Although the rutile structure of TiO is stable at high temperatures, the
conventional quasiharmonic approximation predicts that several acoustic phonons
decrease anomalously to zero frequency with thermal expansion, incorrectly
predicting a structural collapse at temperatures well below 1000\,K. Inelastic
neutron scattering was used to measure the temperature dependence of the phonon
density of states (DOS) of rutile TiO from 300 to 1373\,K. Surprisingly,
these anomalous acoustic phonons were found to increase in frequency with
temperature. First-principles calculations showed that with lattice expansion,
the potentials for the anomalous acoustic phonons transform from quadratic to
quartic, stabilizing the rutile phase at high temperatures. In these modes, the
vibrational displacements of adjacent Ti and O atoms cause variations in
hybridization of electrons of Ti and electrons of O atoms. With
thermal expansion, the energy variation in this "phonon-tracked hybridization"
flattens the bottom of the interatomic potential well between Ti and O atoms,
and induces a quarticity in the phonon potential.Comment: 7 pages, 6 figures, supplemental material (3 figures
Diversification and hybridization in firm knowledge bases in nanotechnologies
The paper investigates the linkages between the characteristics of
technologies and the structure of a firms' knowledge base. Nanotechnologies
have been defined as converging technologies that operate at the nanoscale, and
which require integration to fulfill their economic promises. Based on a
worldwide database of nanofirms, the paper analyses the degree of convergence
and the convergence mechanisms within firms. It argues that the degree of
convergence in a firm's nano-knowledge base is relatively independent from the
size of the firm's nano-knowledge base. However, while firms with small
nano-knowledge bases tend to exploit convergence in each of their
patents/publications, firms with large nano-knowledge bases tend to separate
their nano-R&D activities in the different established fields and achieve
diversity through the juxtaposition of the output of these independent
activitie
Phonon Density of States and Anharmonicity of UO2
Phonon density of states (PDOS) measurements have been performed on
polycrystalline UO2 at 295 and 1200 K using time-of-flight inelastic neutron
scattering to investigate the impact of anharmonicity on the vibrational
spectra and to benchmark ab initio PDOS simulations performed on this strongly
correlated Mott-insulator. Time-of-flight PDOS measurements include anharmonic
linewidth broadening inherently and the factor of ~ 7 enhancement of the oxygen
spectrum relative to the uranium component by the neutron weighting increases
sensitivity to the oxygen-dominated optical phonon modes. The first-principles
simulations of quasi-harmonic PDOS spectra were neutron-weighted and
anharmonicity was introduced in an approximate way by convolution with
wavevector-weighted averages over our previously measured phonon linewidths for
UO2 that are provided in numerical form. Comparisons between the PDOS
measurements and the simulations show reasonable agreement overall, but they
also reveal important areas of disagreement for both high and low temperatures.
The discrepancies stem largely from an ~ 10 meV compression in the overall
bandwidth (energy range) of the oxygen-dominated optical phonons in the
simulations. A similar linewidth-convoluted comparison performed with the PDOS
spectrum of Dolling et al. obtained by shell-model fitting to their historical
phonon dispersion measurements shows excellent agreement with the
time-of-flight PDOS measurements reported here. In contrast, we show by
comparisons of spectra in linewidth-convoluted form that recent
first-principles simulations for UO2 fail to account for the PDOS spectrum
determined from the measurements of Dolling et al. These results demonstrate
PDOS measurements to be stringent tests for ab initio simulations of phonon
physics in UO2 and they indicate further the need for advances in theory to
address lattice dynamics of UO2.Comment: Text slightly modified, results unchange
Innate immune pathways associated with lung radioprotection by soy isoflavones
Introduction: Radiation therapy for lung cancer causes pneumonitis and fibrosis. Soy isoflavones protect against radiation-induced lung injury, but the mediators of radio- protection remain unclear. We investigated the effect of radiation on myeloid-derived suppressor cells (MDSCs) in the lung and their modulation by soy isoflavones for a potential role in protection from radiation-induced lung injury.
Methods: BALB/c mice (5–6 weeks old) received a single 10 Gy dose of thoracic irra- diation and soy isoflavones were orally administrated daily before and after radiation at 1 mg/day. Arginase-1 (Arg-1) and nuclear factor κB (NF-κB) p65 were detected in lung tissue by western blot analysis and immunohistochemistry. Lung MDSC subsets and their Arg-1 expression were analyzed by flow cytometry. Cytokine levels in the lungs were measured by ELISA.
Results: At 1 week after radiation, CD11b+ cells expressing Arg-1 were decreased by radiation in lung tissue yet maintained in the lungs treated with radiation and soy isoflavones. Arg-1 was predominantly expressed by CD11b+Ly6ClowLy6G+ granulocytic MDSCs (gr-MDSCs). Arg-1 expression in gr-MDSCs was reduced by radiation and preserved by supplementation with soy isoflavones. A persistent increase in Arg-1+ cells was observed in lung tissue treated with combined radiation and soy isoflavones at early and late time points, compared to radiation alone. The increase in Arg-1 expression mediated by soy isoflavones could be associated with the inhibition of radiation-induced activation of NF-ÎşB and the control of pro-inflammatory cytokine production demon- strated in this study.
Conclusion: A radioprotective mechanism of soy isoflavones may involve the promotion of Arg-1-expressing gr-MDSCs that could play a role in downregulation of inflammation and lung radioprotection
Effect of Li-deficiency impurities on the electron-overdoped LiFeAs superconductor
We use transport, inelastic neutron scattering, and angle resolved
photoemission experiments to demonstrate that the stoichiometric LiFeAs is an
intrinsically electron-overdoped superconductor similar to those of the
electron-overdoped NaFe1-xTxAs and BaFe2-xTxAs2 (T = Co,Ni). Furthermore, we
show that although transport properties of the stoichiometric superconducting
LiFeAs and Li-deficient nonsuperconducting Li1-xFeAs are different, their
electronic and magnetic properties are rather similar. Therefore, the
nonsuperconducting Li1-xFeAs is also in the electron overdoped regime, where
small Li deficiencies near the FeAs octahedra can dramatically suppress
superconductivity through the impurity scattering effect.Comment: 5 figures,5 page
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