3,360 research outputs found
Electronic structure of YbB: Is it a Topological Insulator or not?
To resolve the controversial issue of the topological nature of the
electronic structure of YbB, we have made a combined study using density
functional theory (DFT) and angle resolved photoemission spectroscopy (ARPES).
Accurate determination of the low energy band topology in DFT requires the use
of modified Becke-Johnson exchange potential incorporating the spin-orbit
coupling and the on-site Coulomb interaction of Yb electrons as large
as 7 eV. We have double-checked the DFT result with the more precise GW band
calculation. ARPES is done with the non-polar (110) surface termination to
avoid band bending and quantum well confinement that have confused ARPES
spectra taken on the polar (001) surface termination. Thereby we show
definitively that YbB has a topologically trivial B 2-Yb 5
semiconductor band gap, and hence is a non-Kondo non-topological insulator
(TI). In agreement with theory, ARPES shows pure divalency for Yb and a -
band gap of 0.3 eV, which clearly rules out both of the previous scenarios of
- band inversion Kondo TI and - band inversion non-Kondo TI. We
have also examined the pressure-dependent electronic structure of YbB,
and found that the high pressure phase is not a Kondo TI but a
\emph{p}-\emph{d} overlap semimetal.Comment: The main text is 6 pages with 4 figures, and the supplementary
information contains 6 figures. 11 pages, 10 figures in total To be appeared
in Phys. Rev. Lett. (Online publication is around March 16 if no delays.
Inclusive Production of Four Charm Hadrons in e^+ e^- Annihilation at B Factories
Measurements by the Belle Collaboration of the exclusive production of two
charmonia in e^+ e^- annihilation differ substantially from theoretical
predictions. Till now, no conclusive explanation for this remarkable
discrepancy has been provided. Even the origin of the discrepancy is not
identified, yet. We suggest that the measurement of four-charm events in Belle
data must provide a strong constraint in identifying the origin of this large
discrepancy. Our prediction of the cross section for e^+e^- -> c c-bar c c-bar,
in lowest order in strong coupling constant, at sqrt{s}=10.6 GeV is about 0.1
pb. If measured four-charm cross section is compatible with the prediction
based on perturbative QCD, it is very likely that factorization of
hadronization process from perturbative part may be significantly violated or
there exists a new production mechanism. If the cross section for the
four-charm event is also larger than the prediction like that for the exclusive
J/psi+eta_c production, perturbative QCD expansion itself will be proved to be
unreliable and loses predictive power.Comment: 4 pages, 3 figures, version published in Phys. Rev. D as a Rapid
Communicatio
Positive Regulation of Myogenic bHLH Factors and Skeletal Muscle Development by the Cell Surface Receptor CDO
AbstractSkeletal myogenesis is controlled by bHLH transcription factors of the MyoD family that, along with MEF-2 factors, comprise a positive feedback network that maintains the myogenic transcriptional program. Cell-cell contact between muscle precursors promotes myogenesis, but little is known of the underlying mechanisms. CDO, an Ig superfamily member, is a component of a cell surface receptor complex found at sites of cell-cell contact that positively regulates myogenesis in vitro. We report here that mice lacking CDO display delayed skeletal muscle development. Additionally, satellite cells from these mice differentiate defectively in vitro. CDO functions to activate myogenic bHLH factors via enhanced heterodimer formation, most likely by inducing hyperphosphorylation of E proteins. The Cdo gene is, in turn, a target of MyoD. The promyogenic effect of cell-cell contact is therefore linked to the activity of myogenic bHLH factors. Furthermore, the myogenic positive feedback network extends from the cell surface to the nucleus
Does Antarctic Krill Employ Body Shrinkage as an Overwintering Strategy?
To determine if Antarctic krill employ body shrinkage as one of its overwintering mechanisms in the field, Euphausia superba and Euphausia crystallorophias were collected during fall and winter in and around Marguerite Bay through US Southern Ocean GLOBEC field programs during fall and winter 2001 and 2002. The relationships between the body length and weight of both krill species were exponentially correlated with no significant differences between the two species (p\u3e0.05). The ratio between eye diameter and body length of individual krill was examined in an expectation that it could be used as an indicator of the body shrinkage as previously suggested by Shin and Nicol (2002). These ratios were significantly different between the two krill species. Especially, E. crystallorophias had bigger eyes than E. superba. In both krill species, eye diameters were highly correlated with body lengths (regression coefficients ≥ 0.70). For E. crystallorophias, no significant differences of the ratio of eye diameter/body length were detected between fall and winter. Even though the ratios for E. superba were seasonally varied, it was not clear whether body shrinkage was an actual and critical overwintering mechanism for the krill population found in this study area. These results suggest that some individuals of E. superba might experience the body shrinkage during a part of their life, but this morphological index alone (eye diameter/body length) may be insufficient to unambiguously separate the shrunk krill from the non-shrunk ones in the field-collected animals
The Cell Surface Membrane Proteins Cdo and Boc Are Components and Targets of the Hedgehog Signaling Pathway and Feedback Network in Mice
SummaryCdo and Boc encode cell surface Ig/fibronectin superfamily members linked to muscle differentiation. Data here indicate they are also targets and signaling components of the Sonic hedgehog (Shh) pathway. Although Cdo and Boc are generally negatively regulated by Hedgehog (HH) signaling, in the neural tube Cdo is expressed within the Shh-dependent floor plate while Boc expression lies within the dorsal limit of Shh signaling. Loss of Cdo results in a Shh dosage-dependent reduction of the floor plate. In contrast, ectopic expression of Boc or Cdo results in a Shh-dependent, cell autonomous promotion of ventral cell fates and a non-cell-autonomous ventral expansion of dorsal cell identities consistent with Shh sequestration. Cdo and Boc bind Shh through a high-affinity interaction with a specific fibronectin repeat that is essential for activity. We propose a model where Cdo and Boc enhance Shh signaling within its target field
- …