2,330 research outputs found
Superconductivity and Electronic Structure of Perovskite MgCNi3
The electronic structure, stability, electron phonon coupling and
superconductivity of the non-oxide perovskite MgCNi are studied using
density functional calculations. The band structure is dominated by a Ni
derived density of states peak just below the Fermi energy, which leads to a
moderate Stoner enhancement, placing MgCNi in the range where spin
fluctuations may noticeably affect transport, specific heat and
superconductivity, providing a mechanism for reconciling various measures of
the coupling . Strong electron phonon interactions are found for the
octahedral rotation mode and may exist for other bond angle bending modes. The
Fermi surface contains nearly cancelling hole and electron sheets that give
unusual behavior of transport quantities particularly the thermopower. The
results are discussed in relation to the superconductivity of MgCNi.Comment: 4 pages, RevTex, 5 ps figure
Derivation of the formyl-group oxygen of chlorophyll b from molecular oxygen in greening leaves of a higher plant (Zea mays)
Using mass spectroscopy, we demonstrate as much as 93% enrichment of the 7-formyl group oxygen of chlorophyll b when dark-grown, etiolated maize leaves are greened under white light in the presence of 18O2. This suggests that a mono-oxygenase is involved in the oxidation of its methyl group precursor. The concomitant enrichment of about 75% of the 131-oxygen confirms the well-documented finding that this oxo group, in both chlorophyll a and b, also arises from O2. High 18O enrichment into the 7-formyl oxygen relative to the substrate 18O2 was achieved by optimization of the greening conditions in combination with a reductive extraction procedure. It indicates not only a single pathway for Chl b formyl group formation, but also unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen
Generation of three iPSC lines from two patients with heterozygous FOXF1 mutations associated to Alveolar Capillary Dysplasia with Misalignment of the Pulmonary Veins
Diagnosing Alveolar Capillary Dysplasia with Misalignment of the Pulmonary Veins (ACD/MPV) based on a genetic alteration in the FOXF1 gene, is complicated by the poor understanding of the causal relation between FOXF1 variants and the ACD/MPV phenotype. Here, we report the generation of human iPSC lines from two ACD/MPV patients, each carrying a different heterozygous FOXF1 mutation, which enables disease modeling for further research on the effect of FOXF1 variants in vitro. The iPSC lines were generated from skin fibroblasts using the non-integrating Sendai virus. The lines expressed pluripotency genes, retained the heterozygous mutation and were capable of trilineage differentiation
Reaming debris as a novel source of autologous bone to enhance healing of bone defects
Item does not contain fulltextReaming debris is formed when bone defects are stabilized with an intramedullary nail, and contains viable osteoblast-like cells and growth factors, and might thus act as a natural osteoinductive scaffold. The advantage of using reaming debris over stem cells or autologous bone for healing bone defects is that no extra surgery is needed to obtain the material. To assess the clinical feasibility of using reaming debris to enhance bone healing, we investigated whether reaming debris enhances the healing rate of a bone defect in sheep tibia, compared to an empty gap. As golden standard the defect was filled with iliac crest bone. Bones treated with iliac crest bone and reaming debris showed larger callus volume, increased bone volume, and decreased cartilage volume in the fracture gap, and increased torsional toughness compared to the empty gap group at 3 weeks postoperative. In addition, bones treated with reaming debris showed increased torsional stiffness at 6 weeks postoperatively compared to the empty defect group, while bending stiffness was marginally increased. These results indicate that reaming debris could serve as an excellent alternative to iliac crest bone for speeding up the healing process in bone defects that are treated with an intramedullary nail
Conductivity sum rule, implication for in-plane dynamics and c-axis response
Recently observed -axis optical sum rule violations indicate non-Fermi
liquid in-plane behavior. For coherent -axis coupling, the observed flat,
nearly frequency independent -axis conductivity implies
a large in-plane scattering rate around and therefore any
pseudogap that might form at low frequency in the normal state will be smeared.
On the other hand incoherent -axis coupling places no restriction on the
value of and gives a more consistent picture of the observed sum rule
violation which, we find in some cases, can be less than half.Comment: 3 figures. To appear in PR
Nature of Correlated Motion of Electrons in the Parent Cobaltate Superconductors
Recently discovered class of cobaltate superconductors (Na0.3CoO2.nH2O) is a
novel realization of interacting quantum electron systems in a triangular
network with low-energy degrees of freedom. We employ angle-resolved
photoemission spectroscopy to uncover the nature of microscopic electron motion
in the parent superconductors for the first time. Results reveal a large
hole-like Fermi surface (consistent with Luttinger theorem) generated by the
crossing of super-heavy quasiparticles. The measured quasiparticle parameters
collectively suggest a two orders of magnitude departure from the conventional
Bardeen-Cooper-Schrieffer electron dynamics paradigm and unveils cobaltates as
a rather hidden class of relatively high temperature superconductors.Comment: 5 pages, 4 figures, 1 tabl
Unitarity and the Bethe-Salpeter Equation
We investigate the relation between different three-dimensional reductions of
the Bethe-Salpeter equation and the analytic structure of the resultant
amplitudes in the energy plane. This correlation is studied for both the
interaction Lagrangian and the system with -, -,
and -channel pole diagrams as driving terms. We observe that the equal-time
equation, which includes some of the three-body unitarity cuts, gives the best
agreement with the Bethe-Salpeter result. This is followed by other 3-D
approximations that have less of the analytic structure.Comment: 17 pages, 8 figures; RevTeX. Version accepted for publication in
Phys. Rev.
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Theoretical study of electronic Raman scattering of Borocarbide superconductors
The electronic Raman scattering of Borocarbide superconductors is studied
based on the weak coupling theory with -wave gap symmetry. The low energy
behaviors and the relative peak positions can be naturally understood, while
the explanation of the detailed shape of the peak seems to require a
strong inelastic interaction not present in the weak coupling theory.Comment: Revtex 4 file, 9 pages and 5 figure
Black Holes from Cosmic Rays: Probes of Extra Dimensions and New Limits on TeV-Scale Gravity
If extra spacetime dimensions and low-scale gravity exist, black holes will
be produced in observable collisions of elementary particles. For the next
several years, ultra-high energy cosmic rays provide the most promising window
on this phenomenon. In particular, cosmic neutrinos can produce black holes
deep in the Earth's atmosphere, leading to quasi-horizontal giant air showers.
We determine the sensitivity of cosmic ray detectors to black hole production
and compare the results to other probes of extra dimensions. With n \ge 4 extra
dimensions, current bounds on deeply penetrating showers from AGASA already
provide the most stringent bound on low-scale gravity, requiring a fundamental
Planck scale M_D > 1.3 - 1.8 TeV. The Auger Observatory will probe M_D as large
as 4 TeV and may observe on the order of a hundred black holes in 5 years. We
also consider the implications of angular momentum and possible exponentially
suppressed parton cross sections; including these effects, large black hole
rates are still possible. Finally, we demonstrate that even if only a few black
hole events are observed, a standard model interpretation may be excluded by
comparison with Earth-skimming neutrino rates.Comment: 30 pages, 18 figures; v2: discussion of gravitational infall, AGASA
and Fly's Eye comparison added; v3: Earth-skimming results modified and
strengthened, published versio
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