University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Changing the resilience paradigm

Abstract: Resilience management goes beyond risk management to address the complexities of large integrated systems and the uncertainty of future threats, especially those associated with climate change.

Observing the Rosensweig instability of a quantum ferrofluid

Abstract: Ferrofluids exhibit unusual hydrodynamic effects owing to the magnetic nature of their constituents. As magnetization increases, a classical ferrofluid undergoes a Rosensweig instability and creates self-organized, ordered surface structures or droplet crystals. Quantum ferrofluids such as Bose-Einstein condensates with strong dipolar interactions also display superfluidity. The field of dipolar quantum gases is motivated by the search for new phases of matter that break continuous symmetries. The simultaneous breaking of continuous symmetries such as the phase invariance in a superfluid state and the translational symmetry in a crystal provides the basis for these new states of matter. However, interaction-induced crystallization in a superfluid has not yet been observed. Here we use in situ imaging to directly observe the spontaneous transition from an unstructured superfluid to an ordered arrangement of droplets in an atomic dysprosium Bose-Einstein condensate. By using a Feshbach resonance to control the interparticle interactions, we induce a finite-wavelength instability and observe discrete droplets in a triangular structure, the number of which grows as the number of atoms increases. We find that these structured states are surprisingly long-lived and observe hysteretic behaviour, which is typical for a crystallization process and in close analogy to the Rosensweig instability. Our system exhibits both superfluidity and, as we show here, spontaneous translational symmetry breaking. Although our observations do not probe superfluidity in the structured states, if the droplets establish a common phase via weak links, then our system is a very good candidate for a supersolid ground state.

PKC zeta is a molecular switch in signal transduction of TNF-alpha, bifunctionally regulated by ceramide and arachidonic acid.

Abstract: Tumor necrosis factor (TNF-alpha) stimulates a number of signal transduction pathways in which phospholipases produce lipid second messengers. However, the immediate molecular targets of these messengers, in particular those of ceramide and arachidonic acid (AA) and their role in TNF signaling are not well defined. In this study we investigated the relationship of ceramide and AA in regulating an atypical PKC isozyme, PKC zeta. U937 cells responding to TNF-alpha treatment with NF kappa B activation displayed enhanced phosphorylation of PKC zeta, which is already detectable 30 s after stimulation. [14C]ceramide specifically binds to and regulates kinase activity of PKC zeta in a biphasic manner. Binding studies indicate high and low affinity binding with bmax values of 60 and 600 nM and Kd values of 7.5 and 320 nM respectively. At ceramide concentrations as low as 0.5 nM an up to 4-fold increase in autophosphorylation is obtained, which, at concentrations > 60 nM, again declines to basal levels. Interestingly, AA competes for ceramide binding and inhibits basal and ceramide-stimulated PKC zeta kinase activity at < 100 nM. Metabolism of [14C]ceramide in cells is slow and is inhibited in the presence of equimolar concentrations of lyso-phosphatidylcholine. Based on the bifunctional modulation of PKC zeta by the lipid messengers ceramide and AA, a model of TNF signal pathways is suggested in which PKC zeta takes a central position, acting as a molecular switch between mitogenic and growth inhibitory signals of TNF-alpha.

Ab initio pseudopotentials for Hg through Rn

Abstract: Quasirelativistic and nonrelativistic energy adjusted ab initio pseudopotentials for the elements Hg through Rn are presented together with corresponding optimized valence basis sets. Core-valence correlation is accounted for by semiempirical polarization potentials. Corrections to the point charge repulsion in the core-nucleus interaction for subsequent molecular calculations are also provided. The reliability of the pseudopotential method is demonstrated in atomic test calculations for electron affinities, excitation and ionization energies as well as spin-orbit splittings by comparison with nonrelativistic, quasirelativistic and relativistic all-electron data. Results obtained by means of two quasirelativistic configuration interaction schemes that include spin-orbit coupling are compared with experimental data.

Strategies for Tracing the Nonlinear Response Near Limit Points

Abstract: For the prebuckling range an extensive literature of effective solution techniques exists for the numerical solution of structural problems but only a few algorithms have been proposed to trace nonlinear response from the pre-limit into the post-limit range. Among these are the simple method of suppressing equilibrium iterations, the introduction of artificial springs, the displacement control method and the “constant-arc-length method” of Riks/Wempner. It is the purpose of this paper to review these methods and to discuss the modifications to a program that are necessary for their implementation. Selected numerical examples show that a modified Riks/Wempner method can be especially recommended.