Stability of autonomous vehicle formations using an ISS small-gain theorem for networks

We consider a formation of vehicles moving on the two dimensional plane. The movement of each vehicle is described by a system of ordinary differential equations with inputs. The formation is maintained using autonomous controls that are designed to maintain fixed relative distances and orientations between vehicles. Moreover this formation should track a given trajectory on the plane. The vehicles can measure the relative distances and angles to their neighbors. These values are the inputs from one system to another. With the help of a general ISS small–gain theorem for networks we will show that the dynamics of such a formation is stable for the given controls. The notion of local input–to– state stability (local ISS) will be used for this purpose. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gradient induced motion control of drifting solitary structures in a nonlinear optical single feedback experiment

We realize an absolute position control of drifting dissipative optical solitons by injecting an incoherent amplitude parameter gradient onto the nonlinear optical system. This allows for two-dimensional, arbitrary control patterns. The control of the soliton drift velocity is studied applying a periodic, hexagonally shaped modulation. The guiding of dissipative solitons by one- and two-dimensional parameter modulations is demonstrated. Furthermore, one-dimensional, line-shaped parameter modulations are designed to act as barriers for dissipative solitons, allowing implementations of position selectors for solitons. The interaction of dissipative optical solitons with barriers is studied for different barrier parameters.     

Nonlinear photonic crystals near the supercollimation point

We uncover a strong coupling between nonlinearity and diffraction in a photonic crystal at the supercollimation point. We show that this is modeled by a nonlinear diffraction term in a nonlinear-Schr?dinger-type equation in which the properties of solitons are investigated. Linear stability analysis shows solitons are stable in an existence domain that obeys the Vakhitov-Kolokolov criterium. In addition, we investigate the influence of the nonlinear diffraction on soliton collision scenarios.     

Virtual crystal approximation study of nitridosilicates and oxonitridoaluminosilicates

We present a density functional theory study of a variety of nitridosilicate and oxonitridoaluminosilicate systems. For the nitridosilicates, we have shown that the DFT-calculated equilibrium structures of BaYb-Si₄N₇, SrYb-Si₄N₇ and EuYb-Si₄N₇ are in good agreement with experiment. We then used the virtual crystal approximation (VCA) to study the effects of oxygen-doping on the nitrogen sites. We then added Si/Al disorder into our system, in order to model the properties of BaYb-SiAlON for pressures up to 50 GPa, in order to investigate recent experimental findings. We have found that this system is stable over the whole pressure range, and that the compression mechanism is pure bond length shortening.     

Violation of the Wiedemann-Franz law in a single-electron transistor

We study the influence of Coulomb interaction on the thermoelectric transport coefficients for a metallic single-electron transistor. By performing a perturbation expansion up to second order in the tunnel-barrier conductance, we include sequential and cotunneling processes as well as quantum fluctuations that renormalize the charging energy and the tunnel conductance. We find that Coulomb interaction leads to a strong violation of the Wiedemann-Franz law: the Lorenz ratio becomes gate-voltage dependent for sequential tunneling, and is increased by a factor 9/5 in the cotunneling regime. Finally, we suggest a measurement scheme for an experimental realization.     

Molecular basis for turnover inefficiencies (misses) during water oxidation in photosystem II

Photosynthesis stores solar light as chemical energy and efficiency of this process is highly important. The electrons required for CO₂ reduction are extracted from water in a reaction driven by light-induced charge separations in the Photosystem II reaction center and catalyzed by the CaMn₄O₅-cluster. This cyclic process involves five redox intermediates known as the S₀–S₄ states. In this study, we quantify the flash-induced turnover efficiency of each S state by electron paramagnetic resonance spectroscopy. Measurements were performed in photosystem II membrane preparations from spinach in the presence of an exogenous electron acceptor at selected temperatures between −10 °C and +20 °C and at flash frequencies of 1.25, 5 and 10 Hz. The results show that at optimal conditions the turnover efficiencies are limited by reactions occurring in the water oxidizing complex, allowing the extraction of their S state dependence and correlating low efficiencies to structural changes and chemical events during the reaction cycle. At temperatures 10 °C and below, the highest efficiency (i.e. lowest miss parameter) was found for the S₁ → S₂ transition, while the S₂ → S₃ transition was least efficient (highest miss parameter) over the whole temperature range. These electron paramagnetic resonance results were confirmed by measurements of flash-induced oxygen release patterns in thylakoid membranes and are explained on the basis of S state dependent structural changes at the CaMn₄O₅-cluster that were determined recently by femtosecond X-ray crystallography. Thereby, possible “molecular errors” connected to the e⁻ transfer, H⁺ transfer, H₂O binding and O₂ release are identified.

Temperature dependence of the transition inefficiencies (misses) for the water oxidation process in photosystem II were studied by EPR spectroscopy and are explained on the basis of S state dependent structural changes at the CaMn₄O₅-cluster.     

Bivalent polyether ionophores: Synthesis and biological evaluation of C2-symmetric salinomycin dimers

Efficient methods for the synthesis of C₂-symmetric dimers of salinomycin joined at either the C1 or C20 positions are reported. Similarly to the native structure, the C20-O-terephthalate dimer displayed activity in the low μM range against a series of cancer cell lines, while dimers joined at the C1 position were essentially inactive.     

Redemitting BODIPY boronic acid fluorescent sensors for detection of lactate

Two redemitting BODIPY boronic acid pinacolate derivatives, sensors 1 and 2 were shown to act as excellent and highly selective lactate detectors at physiological pH (7.4), where the formed sensor-lactate complexes exhibited a significant emission and absorption increase. Since hyperlactataemia ([l-lac] > 6.5 mM) is a common complication in intensive care units, there is need for easy, on-line monitoring of lactate levels in patients. Semi-invasive monitoring via a lactate electrode or optic fiber would be attractive. This may beneficially replace existing lactate detection methods requiring a high degree of instrumentation. Sensors 1 and 2 can detect lactate without interference from biological important monosaccharides, such as d-glucose, d-fructose and d-mannose.