Asymmetric [3 + 2] annulations catalyzed by a planar-chiral derivative of DMAP

A planar-chiral DMAP derivative catalyzes an intriguing [3 + 2] annulation reaction of silylated indenes to produce diquinanes that bear three contiguous stereocenters (one quaternary and two tertiary).     

Estimation of the conformal factor under bounded Willmore energy

We prove for closed, orientable surfaces in $\ \mathbb{R }^3\ $ with Willmore energy less that $\ 8 \pi - \delta \ $ and whose conformal structures are compactly contained in moduli space that after applying appropriate Möbius transformations the conformal factors between the induced metrics and conformal metrics of constant curvature are uniformly bounded by constants depending only on $\ \delta > 0,$ the genus of the surfaces and the compact subset of the moduli space. Secondly, for a given sequence of closed, orientable surfaces as above, we prove that the conformal factor remains bounded without applying Möbius transformations if and only if no topology is lost. Similar estimates hold in higher codimension.     

Search for magnetic interaction in In doped AlN using perturbed angular correlation spectroscopy

The possible presence of a large magnetic field due to spin polarization of a Cd nucleus (decay product of ¹¹¹In) at an Al substitutional site in AlN is investigated with perturbed angular correlation (PAC) spectroscopy. The PAC spectra of ¹¹¹In/¹¹¹Cd in AlN show two probe environments: a weak quadrupole interaction (quadrupole interaction constant, $\nu _{\rm Q}^{\,\,\,\rm lattice} = 30$  MHz) due to ¹¹¹In probes at a defect free Al substitutional site and an unknown large interaction ( $\nu _{\rm Q}^{\,\,\,\rm complex} = 300$  MHz) tentatively attributed to a nearest neighbour pair between ¹¹¹In and a nitrogen vacancy (V_N) aligned along the c-axis. Surprisingly, in density functional theory (DFT) calculations, such a large electric field gradient (EFG) could not be reproduced. However, an inclusion of spin polarization in the calculations indicates a strong magnetic field at ~50 % of the ¹¹¹In/¹¹¹Cd site. An attempt to verify the presence of the strong magnetic field and to explain the origin of the strong interaction is made. Orientation measurements show, the large interaction is not characterised by a magnetic interaction and is predominantly due to the EFG. However, in the presence of an external magnetic field, the strong interaction probe environment becomes more uniform and the EFG increases by ~10 %. This definitely hints towards some sort of magnetic interaction at the strong interaction probe site.     

CFD-simulation of a circulating fluidized bed riser

In the current work,a model of the fluid mechanics in the riser of a circulating fluidized bed(CFB)has been implemented using computational fluid dynamics(CFD).The model developed shall be used in future as the basis of 3D-reactor model for the simulation of large scale CFB combustors.The two-fluid model(TFM)approach is used to represent the fluid mechanics involved in the flow.The computational implementation is accomplished by the commercial software FLUENT.Different closure formulations are tested on a simplified geometry.Two different turbulence formulations,namely the swirl modified RNG k–εmodel and the Realizable k–εmodel,are tested in combination with two different approaches to solid phase turbulence,namely the dispersion and per phase approach.One focus of the current work is put on the study of different drag correlations.Besides the drag correlations by Syamlal et al.[Syamlal,M.,Rogers, W.,O’Brien,T.J.(1993).MFIX documentation theory guide.Technical Report DOE/METC-94/1004,U.S. Department of Energy(DOE).Morgantown Energy Technology Center:Morgantown,WV]and Gidaspow [Gidaspow,D.(1994).Multiphase flow and fluidization.New York:Academic Press]the EMMS model has been used to determine the momentum exchange between the two phases.The resulting formulation is then used to simulate a 1-m×0.3-m cold CFB setup and is validated by experimental results[Schlichthrle, P.(2000).Fluid dynamics and mixing of solids and gas in the bottom zone of circulating fluidized beds. Unpublished doctoral dissertation,Technische Universitaet Hamburg-Harburg,Shaker Verlag:Aachen].     

Cationic rare-earth metal SALEN complexes

Complexes (Salpren(tBu,tBu))Y[N(SiHMe2)2](thf) and (SALEN(tBu,tBu))La[N(SiHMe2)2](thf) (SALEN(tBu,tBu) = Salcyc(tBu,tBu) and Salpren(tBu,tBu)) were prepared from Ln[N(SiHMe2)2]3(thf)2 and H2SALEN(tBu,tBu). The yttrium complex was characterized by X-ray crystallography revealing intrinsic solid-state structural features: the metal centre is displaced by 1.05 angstroms from the [N2O2] least squares plane of a highly bent Salpren(tBu,tBu) ligand (angle(Ph,Ph) dihedral angle of 80.4(1) degrees ) and is coordinated asymmetrically by the silylamide ligand exhibiting one significant Y---(HSi) beta-agostic interaction (Y-N1-Si1, 106.90(9) degrees; Y---Si1, 3.2317(6) angstroms). Complexes (SALEN(tBu,tBu))Ln[N(SiHMe2)2](thf)n (n = 1, Sc; n = 2, Y, La) react with ammonium tetraphenylborate to form the ion pairs [(SALEN(tBu,tBu))Ln(thf)n][BPh4]. The cationisation was proven by X-ray crystal structure analyses of [(Salpren(tBu,tBu))Sc(thf)2][B(C6H5)4].2(thf) and [(Salpren(tBu,tBu))Ln(thf)3][B(C6H5)4].4(thf) (Ln = Y, La), showing an octahedral and pentagonal-bipyramidal coordination geometry, respectively.