Optimal Actuator Placement for Dynamical Systems

Vibrations occur in many industrial areas and produce undesirable side effects. To avoid respectively suppress these effects actuators can be attached to the structure. Actuators can transfer forces into the structure, which can be used to control the system behavior of the structure in order to achieve, for example, vibration absorption, noise reduction and/or exact positioning. The appropriate positioning of actuators is of significant importance for the controllability of the structure. We present a method for determining the optimal actuator placement. We consider applications, where the dynamics of a system can be described by a finite dimensional, controllable and observable state-space model. The concept of controllability by Kálmán forms the basis for the definition of controllability measures. In this context, the controllability gramian plays an important role. In our approach actuators are placed in such a way that the selected controllability measure becomes maximal. This leads to an optimization problem with binary and continuous variables and linear matrix inequalities. The numerical results show the optimal actuator placement for a two dimensional flexible clamped plate. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On algebraic relations for Ramanujan’s functions

Let P,Q, and R denote the Ramanujan Eisenstein series. We compute algebraic relations in terms of P(q ⁱ ) (i=1,2,3,4), Q(q ⁱ ) (i=1,2,3), and R(q ⁱ ) (i=1,2,3). For complex algebraic numbers q with 0<|q|<1 we prove the algebraic independence over ? of any three-element subset of {P(q),P(q ²),P(q ³),P(q ⁴)} and of any two-element subset of {Q(q),Q(q ²),Q(q ³)} and {R(q),R(q ²),R(q ³)}, respectively. For all the results we use some expressions of $P(q^{i_{1}}), Q(q^{i_{2}}) $ , and $R(q^{i_{3}}) $ in terms of theta constants. Computer-assisted computations of functional determinants and resultants are essential parts of our proofs.     

Experimental investigation of the electrokinetic flow in microchannels with internal electrodes

We investigate the electrokinetic flow in microchannels with internal electrodes. Experiments and numerical simulations are performed. The micro–particle–image velocimetry method is used to measure two–dimesional, two–component velocity fields over the complete height of the microchannel. Based on this measurements, the third velocity component, which cannot be measured directly, is calculated by an integration of the continuity equation. Due to the fact that microparticles, used for the μPIV are electrically non-neutral leads to the problem that these particles experience electrophoretic forces. That means that the particle movement appears to be a superposition of electroosmotic and electrophorectic effects. To verify the influence of electrophoretic effects on the microparticles, additional numerical calculations are made. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impact of nongeminate recombination on the performance of pristine and annealed P3HT:PCBM solar cells

Transient photovoltage (TPV) and voltage dependent charge extraction (CE) measurements were applied to poly(3‐hexyl‐thiophene) (P3HT):[6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) bulk heterojunction solar cells to analyze the limitations of solar cell performance in pristine and annealed devices. From the determined charge carrier decay rate under open circuit conditions and the voltage dependent charge carrier densities n (V), the nongeminate loss current j_loss of the device is accessible. We found that j_loss alone is sufficient to describe the j –V characteristics across the whole operational range, for annealed and, not yet shown before, also for the lower performing pristine solar cells. Even in a temperature range from 300 K to 200 K nongeminate recombination is found to be the dominant and, therefore, performance limiting loss process. Consequently, charge photogeneration is voltage independent in the voltage range studied. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Egmont Master phenomenon: X-ray fluorescence spectrometric and paper studies for art history research

The aim of the research project “Typology of Dutch Drawing” was to establish an interdisciplinary approach for investigating heterogeneous drawing collections. To define a type common to a group of drawings, we determine elements that are common to them based on style and the use of identical materials. To that end, we investigated about 750 Dutch drawings from the sixteenth century at the Dresden Kupferstich-Kabinett using art historical and scientific methods. In this work, we present a detailed analysis of 30 drawings ascribed to the Egmont Master.     

Construction of a Microstructured Collagen Membrane Mimicking the Papillary Dermis Architecture and Guiding Keratinocyte Morphology and Gene Expression

A papillary‐structured collagen fibril membrane is created, mimicking the 3D‐architecture of the human papillary dermis. Primary human keratinocytes cultured to confluency on papillar‐structured films are compared to keratinocytes cultured on flat membranes. Microscopical evaluation reveals the presence of morphologically distinct cells at the base of the papillar structures that are not observed on flat membranes. Gene expression microarrays and RT‐qPCR indicate that these cells are in a more proliferative/migrational state, whereas cells on flat membranes have a more differentiated expression profile. Immunohistochemical stainings confirm these results. In conclusion, specific collagen architecture can direct keratinocyte behavior, and this may be used to further improve skin regeneration.

     

Two‐Component In situ Forming Supramolecular Hydrogels as Advanced Biomaterials in Vitreous Body Surgery

Polymeric β‐CD and poly{(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid sodium salt)‐co‐[6‐(acrylamido)‐N‐adamantylhexaneamide]} are synthesized to build in situ forming hydrogels based on host/guest interactions, so called physical hydrogels. The use of these hydrogels as a potential vitreous body substitute is discussed and recommended. Potential changes in cell morphology and cell vitality of the retinal ganglion cell line RGC‐5 are determined. DSC experiments with artificial membrane structures are performed. The analyses show that β‐CD overrides the harmful effects of the highly toxic adamantyl‐modified polymer. Although the final hydrogel is considered to be biocompatible, the application as a biomaterial has to be reconsidered.

     

Adelic geometry and polarity

In the present paper we generalise transference theorems from the classical geometry of numbers to the geometry of numbers over the ring of adeles of a number field. To this end we introduce a notion of polarity for adelic convex bodies.     

Improved broad-spectrum antibiotics against Gram-negative pathogens via darobactin biosynthetic pathway engineering

The development of new antibiotics is imperative to fight increasing mortality rates connected to infections caused by multidrug-resistant (MDR) bacteria. In this context, Gram-negative pathogens listed in the WHO priority list are particularly problematic. Darobactin is a ribosomally produced and post-translationally modified bicyclic heptapeptide antibiotic selectively killing Gram-negative bacteria by targeting the outer membrane protein BamA. The native darobactin A producer Photorhabdus khanii HGB1456 shows very limited production under laboratory cultivation conditions. Herein, we present the design and heterologous expression of a synthetically engineered darobactin biosynthetic gene cluster (BGC) in Escherichia coli to reach an average darobactin A production titre of 13.4 mg L⁻¹. Rational design of darA variants, encoding the darobactin precursor peptide with altered core sequences, resulted in the production of 13 new ‘non-natural’ darobactin derivatives and 4 previously hypothetical natural darobactins. One of the non-natural compounds, darobactin 9, was more potent than darobactin A, and showed significantly improved activity especially against Pseudomonas aeruginosa (0.125 μg mL⁻¹) and Acinetobacter baumannii (1–2 μg mL⁻¹). Importantly, it also displayed superior activity against MDR clinical isolates of E. coli (1–2 μg mL⁻¹) and Klebsiella pneumoniae (1–4 μg mL⁻¹). Independent deletions of genes from the darobactin BGC showed that only darA and darE, encoding a radical forming S-adenosyl-l-methionine-dependent enzyme, are required for darobactin formation. Co-expression of two additional genes associated with the BGCs in hypothetical producer strains identified a proteolytic detoxification mechanism as a potential self-resistance strategy in native producers. Taken together, we describe a versatile heterologous darobactin platform allowing the production of unprecedented active derivatives in good yields, and we provide first experimental evidence for darobactin biosynthesis processes.

Heterologous expression of a synthetically engineered darobactin gene cluster in E. coli yields new darobactin derivatives with improved anti-Gram-negative activity. Targeted gene deletions provide first insights into biosynthetic steps.