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.

Nominal stability of real-time iteration scheme for nonlinear model predictive control

Abstract: A Newton-type method is investigated for online optimisation in nonlinear model predictive control, the so-called real-time iteration scheme. Only one Newton-type iteration is performed per sampling instant in this scheme, and control of the system and the solution of the optimal control problem are performed in parallel. In the resulting combined dynamics of system and optimiser, the actual feedback control in each step is based on the current solution estimate, and the solution estimates are at each sampling instant refined and transferred to the next optimisation problem by a specially designed transition. This approach yields an efficient online optimisation algorithm that has already been successfully tested in several applications. Due to the close dovetailing of system and optimiser dynamics, however, stability of the closed-loop system is not implied by standard nonlinear model predictive control results. A proof of nominal stability of the scheme is given which builds on concepts from both NMPC stability theory and convergence analysis of Newton-type methods. The principal result is that, under some reasonable assumptions, the combined system-optimiser dynamics can be guaranteed to converge towards the origin from significantly disturbed system-optimiser states.

Some aspects of the genesis of structures

Abstract: Bendsoe and Kikuchi (1988) introduced a novel approach of distributing mass within a specified design domain utilizing a stiffness-density relation obtained by homogenization of a cellular microstructure This approach was extended to multiple loading cases and three-dimensional applications by the author and his associates (Mlejnek and Schirrmacher 1989; Mlejnek 1990) Moreover the well-known concept of explicit convex behaviour approximation together with a dual solution scheme (Fleury and Smaoui 1988) was successfully introduced to this problem Further objectives such as eigenvalues and displacements generalized the range of application It is the aim of this paper, to develop a simplified procedure that can be easily integrated into a FEM-analysis package Its application requires essentially not much more than the usual FEM-technology Nevertheless a traceable mathematical base is still maintained A series of examples demonstrates the suitability of this approach to the preliminary design of minimal compliance structures made of isotropic materials

Revealing the subfemtosecond dynamics of orbital angular momentum in nanoplasmonic vortices

Abstract: The ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted much interest. The physical properties of light with a helical wavefront can be confined onto two-dimensional surfaces with subwavelength dimensions in the form of plasmonic vortices, opening avenues for thus far unknown light-matter interactions. Because of their extreme rotational velocity, the ultrafast dynamics of such vortices remained unexplored. Here we show the detailed spatiotemporal evolution of nanovortices using time-resolved two-photon photoemission electron microscopy. We observe both long- and short-range plasmonic vortices confined to deep subwavelength dimensions on the scale of 100 nanometers with nanometer spatial resolution and subfemtosecond time-step resolution. Finally, by measuring the angular velocity of the vortex, we directly extract the OAM magnitude of light.

Cell death stages in single apoptotic and necrotic cells monitored by Raman microspectroscopy

Abstract: Although apoptosis and necrosis have distinct features, the identification and discrimination of apoptotic and necrotic cell death in vitro is challenging. Immunocytological and biochemical assays represent the current gold standard for monitoring cell death pathways; however, these standard assays are invasive, render large numbers of cells and impede continuous monitoring experiments. In this study, both room temperature (RT)-induced apoptosis and heat-triggered necrosis were analyzed in individual Saos-2 and SW-1353 cells by utilizing Raman microspectroscopy. A targeted analysis of defined cell death modalities, including early and late apoptosis as well as necrosis, was facilitated based on the combination of Raman spectroscopy with fluorescence microscopy. Spectral shifts were identified in the two cell lines that reflect biochemical changes specific for either RT-induced apoptosis or heat-mediated necrosis. A supervised classification model specified apoptotic and necrotic cell death based on single cell Raman spectra. To conclude, Raman spectroscopy allows a non-invasive, continuous monitoring of cell death, which may help shedding new light on complex pathophysiological or drug-induced cell death processes.