The Hermitian Laplace Operator on Nearly Kähler Manifolds

The moduli space ${\mathcal {NK}}The moduli space NK{\mathcal {NK}} of infinitesimal deformations of a nearly K?hler structure on a compact 6-dimensional manifold is described by a certain eigenspace of the Laplace operator acting on co-closed primitive (1, 1) forms (cf. Moroianu et al. in Pacific J Math 235:57–72, 2008). Using the Hermitian Laplace operator and some representation theory, we compute the space NK{\mathcal {NK}} on all 6-dimensional homogeneous nearly K?hler manifolds. It turns out that the nearly K?hler structure is rigid except for the flag manifold F(1, 2) = SU₃/T ², which carries an 8-dimensional moduli space of infinitesimal nearly K?hler deformations, modeled on the Lie algebra \mathfraksu₃{\mathfrak{su}_3} of the isometry group.     

Cerebrospinal fluid promotes survival and astroglial differentiation of adult human neural progenitor cells but inhibits proliferation and neuronal differentiation

Background  

Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Growing evidence suggests an important role of cerebrospinal fluid (CSF) not only on neuroectodermal cells during brain development but also on the survival, proliferation and fate specification of NSCs in the adult brain. Existing in vitro studies focused on embryonic cell lines and embryonic CSF. We therefore studied the effects of adult human leptomeningeal CSF on the behaviour of adult human NSCs (ahNSCs).     

Shielding gas influences on laser weldability of tailored blanks of advanced automotive steels

The effects of shielding gas types and flow rates on CO₂ laser weldability of DP600/TRIP700 steel sheets were studied in this work. The evaluated shielding gases were helium (He), argon (Ar) and different mixtures of He and Ar. Weld penetration, tensile strength and formability (Erichsen test) of laser welds were found to be strongly dependent upon the shielding gas types. The ability of shielding gas in removing plasma plume and thus increasing weld penetration is believed to be closely related to ionization potential and atomic weight which determine the period of plasma formation and disappearance. It was found that the higher helium shielding gas flow rate, the deeper weld penetration and the lower weld width.     

Synthesis and electrochemical characterization of nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes

Nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes (N-MWCNTs and N–P-MWCNTs, respectively) were fabricated by chemical vapor deposition and characterized using scanning electron microscopy and transmission electron microscopy in combination with energy dispersive X-ray spectroscopy and Raman spectroscopy. The electrochemical response of N-MWCNTs and N–P-MWCNTs towards ferrocyanide/ferricyanide was initially studied. The findings exhibit weakening of electrochemical response and sensitivity of nanotubes with phosphorus doping, and thus, within the composite films tested, those consist exclusively of N-MWCNTs exhibit the greatest electrocatalytic activity. N–P-MWCNT film was further applied for individual electrochemical analysis of ascorbic acid (AA), uric acid (UA), and dopamine (DA), and lower limits of detections of 11.6, 7.8, and 1.9 μM were estimated, respectively. The findings demonstrate that AA does not interfere with UA, but considerable interference of AA in analysis of DA was observed. Thus, the simultaneous analysis of AA, UA, and DA on N–P-MWCNTs appears to be restricted.     

Efficient coupling of the inhomogeneous current spreading model to the dynamic electro-optical solver for broad-area edge-emitting semiconductor devices

We extend a 2 (space) + 1 (time)-dimensional traveling wave model for broad-area edge-emitting semiconductor lasers by a model for inhomogeneous current spreading from the contact to the active zone of the laser. To speedup the performance of the device simulations, we suggest and discuss several approximations of the inhomogeneous current density in the active zone.     

Optical Transmittance and Band Gap of Ferroelectric BaTi2O5 Bulk Glass

Optical transmittance and reflectance on ferroelectric BaTi₂O₅ glasses prepared recently by a containerless synthesis technique are measured at room temperature in the wavelength range 190-800nm. The fundamental absorption edge located around 340nm demonstrates the colourless and transparent character of the glass. The optical band gap of 3.32eV has been estimated. The tail of the optical absorption near the fundamental absorption edge is found to follow the Urbach rule. Our analysis of the experimental spectra supports an indirect allowed interband transition between the valence band formed by O-2p orbitals and the conduction band formed by Ti-3d orbitals.     

Size-dependent intrinsic radiative decay rates of silicon nanocrystals at large confinement energies

We study ultrafast photoluminescence (PL) dynamics of Si nanocrystals (NCs). The early-time PL spectra (<1 ns), which show strong dependence on NC size, are attributed to emission involving NC quantized states. The PL spectra recorded for long delays (>10 ns) are almost independent of NC size and are likely due to surface-related recombination. Based on instantaneous PL intensities measured 2 ps after excitation, we determine intrinsic radiative rate constants for NCs of different sizes. These constants sharply increase for confinement energies greater than approximately 1 eV indicating a fast, exponential growth of the oscillator strength of zero-phonon, pseudodirect transitions.     

Mononukleare Kupfer(II)‐Komplexe von dioxaalkylenund alkylenverbrückten Bis‐isoharnstoffen

Mononuclear Copper(II) Complexes of Dioxaalkylene and Alkylene Bridged Bis‐isoureas By reaction of N‐benzoylthiocarbamic‐O,S‐diethylester with primary diamines (oxa)alkylene bridged isoureas 1 have been prepared. They yield with Cu^II neutral chelates 2 with tetradentate ligand coordination. The structures of the ligand 1 a and of the related Cu^II complex 2 a have been determined by X‐ray crystal structure analysis. They show an enamine tautomer in the ligand and a slightly tetrahedrally distorted coordination with an (oxa)alkylene bridge between the trans arranged N ligator atoms in the complex.