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Würzburg, Germany

Krause C.,Center for Biomedical Genetics | Korchynskyi O.,Center for Biomedical Genetics | Korchynskyi O.,University of Amsterdam | Weidauer S.E.,UniversitatWurzburg | And 7 more authors.
Journal of Biological Chemistry | Year: 2010

Sclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to antagonize bone morphogenetic protein (BMP) and/or Wnt activity, although at present the underlying mechanisms are unclear. Consistent with previous findings, Sclerostin opposed direct Wnt3a-induced but not direct BMP7-induced responses when both ligand and antagonist were provided exogenously to cells. However, we found that when both proteins are expressed in the same cell, sclerostin can antagonize BMP signaling directly by inhibiting BMP7 secretion. Sclerostin interacts with both the BMP7 mature domain and pro-domain, leading to intracellular retention and proteasomal degradation of BMP7. Analysis of sclerostin knock-out mice revealed an inhibitory action of sclerostin on Wnt signaling in both osteoblasts and osteocytes in cortical and cancellous bones. BMP7 signaling was predominantly inhibited by sclerostin in osteocytes of the calcaneus and the cortical bone of the tibia. Our results suggest that sclerostin exerts its potent bone catabolic effects by antagonizing Wnt signaling in a paracrine and autocrine manner and antagonizing BMP signaling selectively in the osteocytes that synthesize simultaneously both sclerostin and BMP7 proteins. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc. Source

Schmidt W.,University of Gottingen | Schmidt W.,UniversitatWurzburg | Kern S.A.W.,UniversitatWurzburg | Kern S.A.W.,Max Planck Institute for Astronomy | And 3 more authors.
Astronomy and Astrophysics | Year: 2010

Context. Supersonic turbulence in the interstellar medium plays an important role in the formation of stars. The origin of this observed turbulence and its impact on the stellar initial mass function (IMF) still remain open questions. Aims. We investigate the influence of the turbulence forcing on the mass distributions of gravitationally unstable cores in simulations of isothermal supersonic turbulence. Methods. Data from two sets of non-selfgravitating hydrodynamic FLASH3 simulations with external stochastic forcing are analysed, each with static grid resolutions of 2563, 5123 and 10243 grid points. The first set applies solenoidal (divergence-free) forcing, while the second set uses purely compressive (curl-free) forcing to excite turbulent motions. From the resulting density field, we compute the mass distribution of gravitationally unstable cores by means of a clump-finding algorithm. Using the time-averaged probability density functions of the mass density, semi-analytic mass distributions are calculated from analytical theories. We apply stability criteria that are based on the Bonnor-Ebert mass resulting from the thermal pressure and from the sum of thermal and turbulent pressure. Results. Although there are uncertainties in applying of the clump-finding algorithm, we find systematic differences in the mass distributions obtained from solenoidal and compressive forcing. Compressive forcing produces a shallower slope in the high-mass power-law regime compared to solenoidal forcing. The mass distributions also depend on the Jeans length resulting from the choice of the mass in the computational box, which is freely scalable for non-selfgravitating isothermal turbulence. If the Jeans length corresponding to the density peaks is less than the grid cell size, the distributions obtained by clump-finding show a strong resolution dependence. Provided that all cores are numerically resolved and most cores are small compared to the length scale of the forcing, the normalised core mass distributions are close to the semi-analytic models. Conclusions. The driving mechanism of turbulence has a potential impact on the shape of the core mass function. Especially for the high-mass tails, the Hennebelle-Chabrier theory implies that the additional support due to turbulent pressure is important. © 2010 ESO. Source

Geelhaar L.,Qimonda AG | Geelhaar L.,Paul Drude Institute for Solid State Electronics | Cheze C.,Qimonda AG | Cheze C.,Paul Drude Institute for Solid State Electronics | And 16 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2011

On Si(111) and Si(001), GaN nanowires (NWs) form in a self-induced way without the need for any external material. On sapphire, NW growth is induced by Ni collectors. Both types of NWs exhibit the wurtzite crystal structure and grow in the Ga-polar C-direction perpendicular to the substrate. The NW sidewalls are M-plane facets, although on the Ni-induced NWs also A-plane segments form, if the growth temperature is low. Both self-induced and collector-induced NWs are free of strain and epitaxially aligned to the substrate, but in particular the former show a significant spread in tilt and twist caused by a mostly amorphous interfacial layer of Si-N. The self-induced NWs are virtually free of extended defects, but the collector-induced NWs contain many stacking faults. The photoluminescence of the former is significantly brighter and sharper. The spectra of single, dispersed, self-induced NWs contain extremely sharp excitonic lines. Significant emission is caused by excitons bound to donors close to the surface whose binding energy is reduced compared to the bulk value. In comparison, both the microstructure and optical properties of the self-induced NWs are superior. The limited material quality of the collector-induced NWs can be explained by detrimental effects of the collector. © 2011 IEEE. Source

Patrakov A.E.,UniversitatWurzburg | Fink R.F.,UniversitatWurzburg | Fink K.,Karlsruhe Institute of Technology | Schmidt T.C.,UniversitatWurzburg | Engels B.,UniversitatWurzburg
Physica Status Solidi (B) Basic Research | Year: 2010

We present a density-functional study on the mobility of cadmium (Cd) and tellurium (Te) adsorbate atoms on the reconstructed Te-terminated (001) CdTe (2 × 1) surface. Two-dimensional potential energy surfaces as a function of the position of the adsorbate atom on the surface were calculated. For Cd as well as Te adsorption, two potential minima were found. The binding energies amount to -2. and -0.71 eV for Cd (-2.8 and -1.4 eV for Te). At any position of the surface, Te adsorption is found to be stronger than that of Cd. Our results indicate that an adsorption of a Te atom at the reconstructed Te-terminated (001) CdTe (2 × 1) surface leads to adsorbates which may move along the surface due to their thermal energy. In the opposite, Cd adsorbate atoms are essentially trapped in the global minimum and desorption is expected to be much more likely than motion along the surface. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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