Degenerate cases of stability loss of an elastic fluid-conveying tube

The two-dimensional non-linear dynamics of a liquid-filled tube is considered. The tube is clamped at the upper end, a point mass is fixed to its free lower end and laterally it is supported by two springs. The uniform flow velocity of the fluid, the end mass, the spring constant and the vertical position of the springs are considered as the distinguished parameters of the problem. A linear stability analysis shows that the (degenerate) case of a Takens-Bogdanov-Hopf bifurcation exists, which is associated with a high frequency flutter movement superimposed on a low frequency flutter around a statically buckled state of the tube. We account for this degenerate case by indicating the parameter regime necessary for its occurence and and give the bifurcation diagram for the trivial equilibrium position of the tube. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of symbolical kinematics for the efficient solution of force workspace of excavators

This paper describes a method for the efficient determination of maximally allowed shovel forces for a heavy-load faceshovel excavator through its workspace, based on the concept of “kinematical transformers”. In this concept, each multibody loop is regarded as a transmission element coupled by linear equations with the other multibody loops, allowing an efficient detection of closed-form kinematical solutions. Additionally, the method uses a graphical optimization approach to find the maximal digging forces for given positions of the shovel. An application-specific code has been realized using a combination of the object-oriented multibody library MBILE and symbolical equations. The method is applied to existing heavy-load excavators, showing that by the use of symbolical kinematics, the computational effort can be reduced substantially. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Über die Kondensation von Formisobutyraldol mit Acetaldehyd

Ohne ZusammenfassungAm Schlusse meiner Ausführung angelangt, bitte ich noch meinen verehrten Lehrer Hofrat Adolf Lieben, meinen ergebensten Dank entgegenzunehmen für die freundliche Unterstützung, die er meiner Arbeit durch seine Ratschläge angedeihen ließ, und für das Interesse, das er ihr entgegenbrachte.Auch danke ich hier dem Herrn Privatdozenten Dr. C. Pomeranz für seine freundliche Unterstützung.     

Über das Allylbiguanid und einige seiner Derivate

Ohne Zusammenfassung     

Magnetic phases in UNi<Subscript>2</Subscript>Si<Subscript>2</Subscript>

The tetragonal compound UNi₂Si₂ exhibits in zero magnetic field three different antiferromagnetic phases belowT _N =124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q _z ). Two additional order-order magnetic phase transitions are observed below T _N , namely atT ₁=108 K and T ₂=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi₂Si₂ single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi₂Si₂.     

Two Amphoteric Silver Carbene Clusters

Two highly labile silver carbene cluster complexes are described, which are unique in that they mark the transition point at which the carbene center transmutes from a fairly common NHC‐like nucleophilic behavior to an electrophilic character befitting reactive silver carbene intermediates of relevance in various catalytic transformations. This amphoteric character is the distinguishing attribute of a μ‐bridged donor/donor carbene entity that connects two silver atoms of triangular or tetrahedral metallic core units.     

Collective low-energy excitations of two-level tunnelling defects in mixed crystals

The dynamics of strongly interacting two-level tunnelling defects in mixed crystals as KCl: Li is investigated in the framework of Mori's projection method. Applying a mode-coupling scheme on the memory functions and performing the average over the random defect configuration in a mean-field type approximation, the ensueing self-consistent equations can be solved analytically. At low concentration this solution coincides with the exact dynamics of the pair model, whereas for higher concentration the motional spectrum shows several novel features. In particular we find a strong relaxation peak and a characteristic two-peak structure for the density of states; there is an additional feature at energies far below the bare tunnelling amplitude which accounts well for several experiments indicating the existence of such low-energy states.