Indolalkaloide aus dem blätterpilz cortinarius infractus (agaricales)

From fruit bodies of the gilled agaric $\text{Cortinarius infractus}$ three new β-carboline derivatives infractin (1), 6-hydroxyinfractin (2) and infractopicrin (4) have been isolated. 4 is responsible for the bitter taste of the toadstool.     

Elektronenspektrum und Bildungsenthalpie des Gaskomplexes CrAl2Cl8

Electronic Spectrum and Enthalpy of Formation of the gaseous Complex CrAl₂Cl₈ At 600 K Al₂Cl_6,g reacts with CrCl_2,8 giving the gaseous complex CrAl₂Cl₈. From measurements of the absorption spectrum (v_max = 11.6 kK; ? = 53.01/Mol · cm) it is to conclude that Cr has an octahedral (distorted) Cl coordination. For the equilibrium CrCl_2,s + Al₂Cl_6,g = CrAl₂Cl_8,g at ～600 K the data ΔH° = 9.07 kcal/Mol; ΔS° = 11.0 eu have been derived.     

Novel Unsymmetric α‐Diimine Nickel(II) Complexes: Suitable Catalysts for Copolymerization Reactions

We established a strategy to synthesize novel unsymmetric 2,3‐diaza‐1,4‐dithiane ligands. Reaction of [Ni(acac)₂] and trityl tetrakis(pentafluorophenyl)borate in the presence of these ligands afforded the corresponding salt‐type complexes. All new compounds were characterized by means of elemental analysis and NMR spectroscopy, and the complexes additionally by mass spectroscopy. NMR spectroscopic experiments on polymers generated by the symmetric ligand/trimethylaluminum catalyst system showed that all products were nearly linear, independent of the polymerization conditions. By contrast, polymers produced by the unsymmetric ligand/trimethylaluminum catalyst system under homopolymerization conditions were branched (15–24 ‰). Additionally, copolymerization experiments with propylene and 1‐hexene afforded copolymers with a branching level of up to 50 ‰.     

Rainbows in the Hypercube

Let Q_n be a hypercube of dimension n, that is, a graph whose vertices are binary n-tuples and two vertices are adjacent iff the corresponding n-tuples differ in exactly one position. An edge coloring of a graph H is called rainbow if no two edges of H have the same color. Let f(G,H) be the largest number of colors such that there exists an edge coloring of G with f(G,H) colors such that no subgraph isomorphic to H is rainbow. In this paper we start the investigation of this anti-Ramsey problem by providing bounds on f(Q_n,Q_k) which are asymptotically tight for k = 2 and by giving some exact results.     

Simulation of local instabilities during crack propagation in the ductile–brittle transition region

The crack propagation for a cohesive zone model within an elastic-plastic material under small-scale yielding conditions is simulated numerically. The resulting crack growth resistance curves show local instabilities, so-called pop-ins even for homogeneous cohesive properties if the cohesive strength lies sufficiently close to the maximum stress of the corresponding blunting solution. The formation of secondary cracks and unloading zones in front of the actual crack tip is identified as the underlying mechanism. It is found that the shape of the cohesive law has a considerable influence on the crack arrest behavior. Furthermore, requirements to the mesh resolution are derived.     

Constitutive equations for porous plane-strain gradient elasticity obtained by homogenization

This paper addresses the problem of plane-strain gradient elasticity models derived by higher-order homogenization. A microstructure that consists of cylindrical voids surrounded by a linear elastic matrix material is considered. Both plane-stress and plane-strain conditions are assumed and the homogenization is performed by means of a cylindrical representative volume element (RVE) subjected to quadratic boundary displacements. The constitutive equations for the equivalent medium at the macroscale are obtained analytically by means of the Airy’s stress function in conjunction with Fourier series. Furthermore, a failure criterion based on the maximum hoop stress on the void surface is formulated. A mixed finite-element formulation has been implemented into the commercial finite-element program Abaqus. Using the constitutive relations derived, numerical simulations were performed in order to compute the stress concentration at a hole with varying parameters of the constitutive equations. The results predicted by the model are discussed in comparison with the results of the theory of simple materials.     

A novel constitutive law for Silicon under contact loading

Silicon (Si) remains the most important semiconductor material to date. The understanding of its deformation behavior under contact (indenter-) loading is crucial to improving technologically relevant abrasive machining techniques (lapping, sawing, grinding). While it has been long established that Si undergoes a series of stress driven phase transitions upon compression and subsequent pressure release, to the authors' knowledge, no material model is available that adequately captures this behavior. In particular, reverse transformation in unloading has received too little attention. A novel phenomenological, thermomechanical model based on experimental observations and MD predictions is presented in this work. It captures both the cd-Si → β-Si transition upon compression and the β-Si → a-Si transition upon rapid decompression, which are most relevant for indenter loading. To control inelasticity in unloading, the dissipation function was augmented by a kinematic constraint on the tensorial internal variable. In stress space, the transformation surfaces are hyperboloids of revolution aligned along the hydrostatic axis. The non-linear model was numerically implemented in a finite element code using an iterative implicit algorithm and successfully applied to simple loading cases. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthese und Strukturuntersuchung von Zn3Ta2O8

Zn₃Ta₂O₈ was prepared by high temperature solid state reaction (CO₂-Lasertechnique). X-ray investigations of single crystals yield monoclinic symmetry (a=9.499;b=8.411;c=8.881 Å; =116.03°, space group C _2h ⁶ —C2/c). There is no relationship between Zn₃Ta₂O₈ and Zn₃Nb₂O₈. Zn₃Ta₂O₈ shows a characteristic structure type with octahedral coordination of Ta⁵⁺ and tetrahedral coordination of Zn²⁺.

     

Fluxgate magnetorelaxometry of superparamagnetic nanoparticles for hydrogel characterization

A new characterization method for hydrogels based on the relaxation behavior of superparamagnetic nanoparticles (MNPs) is proposed. MNPs are incorporated in the hydrogel to examine its network properties. By analyzing their relaxation behavior, incorporated and mobile nanoparticles can be studied. In the case of mobile nanoparticles, the microviscosity of the hydrogel can be determined. Thus, this method allows the studying of gelation as well as the degradation process of hydrogels. Furthermore, the hydrogel can have any shape (e.g. microspheres or larger blocks) and no sample preparation is needed, avoiding artefacts.     

Synthese und Struktur chiraler Heterometallatetrahedrane des Typs [Re2(M1PPh3)(M2PPh3)(μ‐PCy2)(CO)7C≡CPh] (M1 = Ag,Au; M2 = Cu,Ag, Au)

Syntheses and Structure of Chiral Metallatetrahedron Complexes of the Type [Re₂(M¹PPh₃)(M²PPh₃)(μ‐PCy₂)(CO)₇C≡CPh] (M¹ = Ag, Au; M² = Cu, Ag, Au) From the reaction of Li[Re₂(μ‐H)(μ‐PCy₂)(CO)₇(C(Ph)O)] ( 1 ) with Ph₃AuC≡CPh both benzaldehyde and the trinuclear complex Li[Re₂(AuPPh₃)(μ‐PCy₂)(CO)₇C≡CPh] ( 2a ) were obtained in high yield. The complex anion was isolated as its PPh₄‐salt 2b . The latter reacts with coinage metal complexes PPh₃M²Cl [M² = Cu, Ag, Au] to give chiral heterometallatetrahedranes of the general formula [Re₂(AuPPh₃)(M²PPh₃)(μ‐PCy₂)(CO)₇C≡CPh] (M² = Cu 3a , Ag 3b , Au 3c ). The corresponding complex [Re₂(AgPPh₃)₂(μ‐PCy₂)(CO)₇C≡CPh] ( 3d ) is obtained from the reaction of [Re₂(AgPPh₃)₂(μ‐PCy₂)(CO)₇Cl] ( 4 ) with LiC≡CPh. 3d undergoes a metathesis reaction in the presence of PPh₃CuCl giving [Re₂(AgPPh₃)(CuPPh₃)(μ‐PCy₂)(CO)₇C≡CPh] ( 3e ) and PPh₃AgCl. Analogous metathesis reactions are observed when 3c is reacted with PPh₃AgCl or PPh₃CuCl giving 3a or 3b , respectively. The reaction of 1 with PPh₃AuCl gives benzaldehyde and Li[Re₂(AuPPh₃)(μ‐PCy₂)(CO)₇Cl] ( 5a ) which upon reaction with PhLi forms the trinuclear complex Li[Re₂(AuPPh₃)(μ‐PCy₂)(CO)₇Ph] ( 6a ). Again this complex was isolated as its PPh₄‐salt 6b . In contrast to 2b , 6b reacts with one equivalent of Ph₃PAuCl by transmetalation to give Ph₃PAuPh and PPh₄[Re₂(AuPPh₃)(μ‐PCy₂)(CO)₇Cl] ( 5b ). The X‐ray structures of the compounds 3a , 3b , 3e and 4 are reported.