Publications

We exploit an adaptive control technique, namely funnel control, to establish both initial and recursive feasibility in Model Predictive Control (MPC) for output-constrained nonlinear systems. Moreover, we show that the resulting feedback controller outperforms the funnel controller both w.r.t. the required sampling rate for a zero-order-hold implementation and required control action. We further propose a combination of funnel control and MPC, exploiting the performance guarantees of the model-free funnel controller during a learning phase and the advantages of the model-based MPC scheme thereafter.

The application of double electron-electron resonance (DEER) with site-directed spin labeling (SDSL) to measure distances in proteins and protein complexes in living cells puts rigorous restraints on the spin-label. The linkage and paramagnetic centers need to resist the reducing conditions of the cell. Rigid attachment of the probe to the protein improves precision of the measured distances. Here, three two-armed GdIII complexes, GdIII-CLaNP13a/b/c were synthesized. Rather than the disulfide linkage of most other CLaNP molecules, a thioether linkage was used to avoid reductive dissociation of the linker. The doubly GdIII labeled N55C/V57C/K147C/T151C variants of T4Lysozyme were measured by 95 GHz DEER. The constructs were measured in vitro, in cell lysate and in Dictyostelium discoideum cells. Measured distances were 4.5 nm, consistent with results from paramagnetic NMR. A narrow distance distribution and typical modulation depth, also in cell, indicate complete and durable labeling and probe rigidity due to the dual attachment sites.

Bioactive composite material based on hydroxyapatite (HA), sodium alginate (Alg) with different content of graphene oxide (GO) was synthesized by the wet chemistry method and characterized by TEM, XRD, FTIR, HPLC analysis. Introduced the GO nanoparticles, as well as Ca2+ ions, as cross-linker of Alg macromolecules by the beads formation, lead to enhancement of the composites mechanical properties. HA-Alg-GO10 sample with GO content of 0.004% in relation to the HA powder has a much higher Youngs modulus (1325 MPa) in comparison with GO-free HA-Alg composite (793 MPa), as well as steel sample of the same size (˜706 MPa). The addition of GO reduces the degree of the composites swelling in a phosphate buffered saline for 43% and enhances the beads shape stability. Chlorhexidine bigluconate release from GO containing samples lasts for 48 h longer according to HPLC study. The findings clear demonstrate the potential possibility of applications of the HA-Alg-GO composite material in bioengineering of bone tissue to fill bone defects of various geometries with the function of prolonged release of the drug. It is assumed that HA-Alg-GO composite material can be used in 3D modeling of areas of bone tissue that have to bear a mechanical load.

We are concerned with the design of Model Predictive Control (MPC) schemes such that asymptotic stability of the resulting closed loop is guaranteed - even if the linearization at the desired set point fails to be stabilizable. Therefore, we propose constructing the stage cost based on the homogeneous approximation and rigorously show that applying MPC yields an asymptotically stable closed-loop behavior if the homogeneous approximation is asymptotically null controllable. To this end, we verify cost controllability - a condition relating the current state, the stage cost, and the growth of the value function with respect to time - for this class of systems in order to provide stability and performance guarantees for the proposed MPC scheme without stabilizing terminal costs or constraints.