Tetrylenes chelated by hybrid amido-amino ligand: derivatives of 2-[(N,N-dimethylamino)methyl]aniline

Reaction of 2-[(dimethylamino)methyl]aniline with butyllithium, followed by conversion with trimethylsilyl, triphenylsilyl, triphenylgermyl, trimethylstannyl, or tri-n-butylstannyl chloride, gives the corresponding substituted aniline. These compounds were further deprotonated by butyllithium and reacted with germanium, tin, and lead dichlorides, respectively, in both stoichiometric ratios 2:1 and 1:1, providing the target homo- ([2-(Me(2)NCH(2))C(6)H(4)(YR(3))N](2)M) and heteroleptic ([2-(Me(2)NCH(2))C(6)H(4)(YR(3))N]MCl) germylenes and stannylenes, where M = Ge, Sn, Y = Si, Ge, and R = Me, Ph. Unlike all of these cases, the heteroleptic plumbylene can only be obtained with this reaction when the amide is substituted by a trimethylsilyl moiety. Anilines substituted by trimethyltin or tri-n-butyltin moieties gave transmetalation products after the second deprotonation by butyllithium. The trimethyltin-substituted stannylenes could likewise not be obtained by hexamethyldisilazane elimination of (trimethylstannyl)-2-[(dimethylamino)methyl]aniline with 0.5 mol equiv of either bis[bis(trimethylsilyl)amido]tin or {bis[bis(trimethylsilyl)amido]tin chloride}. Products of these reactions are heterocubanes with compositions {[2-(Me(2)NCH(2))C(6)H(4)N]Sn}(4) and [2-(Me(2)NCH(2))C(6)H(4)N](2)(μ(2)-SnMe(2))(2), respectively, and Me(4)Sn or Me(3)SnCl. The structures of trimethylsilyl- and triphenylgermyl-substituted germylenes, stannylenes, and plumbylenes, as well as a number of their precursors, in the crystalline state, were investigated by X-ray diffraction and NMR spectroscopy in solution. Density functional theory methods were used for evaluation of the structures of several compounds.     

Pressure effect on magnetic moments in ordered Ni3Mn and disordered Ni100−x Mn x alloys: ab initio calculation and experiment

We have revealed a substantial difference in the pressure behavior of magnetization of the ordered Ni₃Mn and the disordered Ni₇₅Mn₂₅ and Ni₈₀Mn₂₀ alloys in the pressure range up to 1.2 GPa. To explain in detail the peculiarities of magnetic properties of the Ni-rich NiMn alloys, the reference electronic structure of the alloys was calculated using the tight-binding linear muffin-tin orbital approach. The effect of disorder was described by the coherent potential approximation. The theoretical ab initio calculations (with changes of the lattice parameters up to 1%) elucidated the pressure stability of the magnetic Mn moments and revealed that the very pronounced decrease in the magnetization of the disordered alloys under pressure is caused by the relatively small change in portion of the Mn moments with parallel and anti-parallel orientation with respect to the total moment. The quantitative agreement with experiment has been reached for the pressure parameters dln M/dP.     

Finite element‐fictitious boundary methods (FEM‐FBM) for 3D particulate flow

In this paper we discuss numerical simulation techniques using a finite element approach in combination with the fictitious boundary method (FBM) for rigid particulate flow configurations in 3D. The flow is computed with a multigrid finite element solver (FEATFLOW), the solid particles are allowed to move freely through the computational mesh which can be static or adaptively aligned by a grid deformation method allowing structured as well as unstructured meshes. We explain the details of how we can use the FBM to simulate flows with complex geometries that are hard to describe analytically. Stationary and time‐dependent numerical examples, demonstrating the use of such geometries are provided. Our numerical results include well‐known benchmark configurations showing that the method can accurately and efficiently handle prototypical particulate flow situations in 3D with particles of different shape and size. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient computation of non-isothermal highly viscous incompressible flow

We consider the numerical solution of the non–isothermal incompressible Navier–Stokes equations using a discrete projection method. The computation of velocity and temperature subproblems is carried out on different meshes chosen with respect to the physical behavior of these quantities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoemission,NMR, susceptibility and specific heat in V and A15 V3Pt

We present a study on the electronic structure of V and V₃Pt, based on photoemission (XPS and UPS) measurements and on the examination of previous band calculations, specific heat, susceptibility and NMR results. Photoemission spectra on pure V, in particular the XPS one, show a good agreement with band calculations ; the He_II spectrum exhibits a strong satellite which could be attributed to a simple Auger effect or to a resonant process. Photoemission on V₃Pt allows an evaluation of the partial densities of states (PDOS) ; the Vanadium PDOS is similar to that of pure element, at least for the upper part of the valence band ; meanwhile the Platinium partial EDOS is drastically modified. This can be understood in the framework of electronic structure of compounds involving early and late transition metals where the atomic structure seems to play an important role. An evaluation of the EDOS's at the Fermi level n(E_F) can also be tempted and compared to those obtained from the other mentioned techniques. Therefore it is suggested that for Vanadium n(E_F) is similar to that of pure element ; for Platinium n(E_F) is strongly reduced. Finally the analysis of the electronic specific heat of V, Pt and V₃Pt indicates that the parameter of electron-phonon coupling determined by the Mc Millan's theory is likely underesti:ated, due to the occurence of an estimated coupling in V and V₃Pt.     

Theory of Electron Transport in FeRh-Based Natural Magnetic Multilayers

The electronic structure and the residual resistivity of random FeRh-based alloys in the CsCl structure are calculated from first principles. The calculations are performed for different spin structures using the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. The effect of late transition-metal impurities (Pd, Rh) is taken into account by means of the coherent potential approximation generalized to inhomogeneous systems. It is shown that impurity scattering leads to giant magnetoresistance effects in qualitative agreement with experiment.     

Exchange Interactions and Curie Temperatures of 3D- and 2D-Ferromagnets

Effective exchange interactions in bulk ferromagnets as well as in magnetic overlayers on Cu(001) covered by a Cu-cap layer of varying thickness were determined from first principles by mapping of corresponding total energies onto the effective Heisenberg model in the framework of the adiabatic approximation and magnetic force theorem. The effective Heisenberg model is then used to determine spin-wave stiffness constants and Curie temperatures evaluated in the framework of the random-phase approximation. Calculations are in a fair agreement with available experimental data for bulk ferromagnets and reproduce an oscillatory Curie temperature of magnetic overlayers as a function of Cu-cap thickness in a qualitative agreement with recent experiments.     

Spin-dependent transparency of ferromagnet/superconductor interfaces

We combine parameter-free calculations of the transmission and reflection matrices for clean and dirty interfaces with a scattering-theory formulation of Andreev reflection (AR) generalized to spin-polarized systems in order to critically evaluate the use of an extended Blonder-Tinkham-Klapwijk (BTK) model to extract values of the spin polarization for ferromagnetic metals from measurements of point-contact AR. Excellent agreement with the experimental conductance data is found for Pb/Cu but it is less good for Pb/Ni and poor for Pb/Co, indicating that the BTK formalism does not describe transport through superconducting/ferromagnetic interfaces correctly.