Averaging in vibration suppression by parametric stiffness excitation

Stability investigations of vibration suppression employing the concept of actuators with a variable stiffness are presented. Systems with an arbitrary number of degrees of freedom with linear spring- and damping-elements are considered that are subject to self-excitation as well as parametric stiffness excitation. General conditions for full vibration suppression and conditions of instability are derived analytically by applying a singular perturbation of first and second order. The analytical predictions are compared for exemplary systems by numerical time integration and show a great improvement of former results. These basic results obtained can be used for accurate design of a control strategy for actuators. The first author gratefully acknowledges the mobility grant of Vienna University of Technology for visiting the University of Utrecht during which preliminary results were obtained.     

Emergence and Bifurcations of Lyapunov Manifolds in Nonlinear Wave Equations

Persistence and bifurcations of Lyapunov manifolds can be studied by a combination of averaging-normalization and numerical bifurcation methods. This can be extended to infinite-dimensional cases when using suitable averaging theorems. The theory is applied to the case of a parametrically excited wave equation. We find fast dynamics in a finite, resonant part of the spectrum and slow dynamics elsewhere. The resonant part corresponds with an almost-invariant manifold and displays bifurcations into a wide variety of phenomena among which are 2- and 3-tori.     

Recycling of isotopically modified molybdenum from irradiated CerMet nuclear fuel: part 3—strontium separation from concentrated molybdate solution

This study is aimed at developing a promising method of strontium impurity separation from concentrated molybdenum solutions originating from molybdenum recycling from irradiated CerMet nuclear fuels with an isotopically tailored molybdenum matrix. Strontium sorption onto thirteen inorganic or composite absorbers from a slightly alkaline (pH 9.1) ammonium molybdate surrogate solution was studied. Based on the evaluation of weight distribution ratios, their dependence on molybdenum concentration and pH, and kinetics of sorption, calcium activated barium sulfate (Ba(Ca)SO₄) was identified as the most promising material. In a dynamic column experiment performed with the Ba(Ca)SO₄-PAN absorber, 2700 BV of the solution with c_Sr = 10⁻⁴ mol L⁻¹ could be treated with a breakthrough of lower than 1% and 100% breakthrough was not achieved even after processing almost 7000 BV of the feed.

     

Chemoenzymatic Total Synthesis of Deoxy‐, epi‐, and Podophyllotoxin and a Biocatalytic Kinetic Resolution of Dibenzylbutyrolactones

Podophyllotoxin is probably the most prominent representative of lignan natural products. Deoxy‐, epi‐, and podophyllotoxin, which are all precursors to frequently used chemotherapeutic agents, were prepared by a stereodivergent biotransformation and a biocatalytic kinetic resolution of the corresponding dibenzylbutyrolactones with the same 2‐oxoglutarate‐dependent dioxygenase. The reaction can be conducted on 2 g scale, and the enzyme allows tailoring of the initial, “natural” structure and thus transforms various non‐natural derivatives. Depending on the substitution pattern, the enzyme performs an oxidative C?C bond formation by C?H activation or hydroxylation at the benzylic position prone to ring closure.     

Computation by Asynchronously Updating Cellular Automata

A known method to compute on an asynchronously updating cellular automaton is the simulation of a synchronous computing model on it. Such a scheme requires not only an increased number of cell states, but also the simulation of a global synchronization mechanism. Asynchronous systems tend to use synchronization only on a local scale—if they use it at all. Research on cellular automata that are truly asynchronous has been limited mostly to trivial phenomena, leaving issues such as computation unexplored. This paper presents an asynchronously updating cellular automaton that conducts computation without relying on a simulated global synchronization mechanism. The two-dimensional cellular automaton employs a Moore neighborhood and 85 totalistic transition rules describing the asynchronous interactions between the cells. Despite the probabilistic nature of asynchronous updating, the outcome of the dynamics is deterministic. This is achieved by simulating delay-insensitive circuits on it, a type of asynchronous circuit that is known for its robustness to variations in the timing of signals. We implement three primitive operators on the cellular automaton from which any arbitrary delay-insensitive circuit can be constructed and show how to connect the operators such that collisions of crossing signals are avoided.     

Massenspeaktrometrische Untersuchungen zur Ketenabspaltung aus Zimtalkohol

The elimination of ketene from the molucular ion of cinnamic alchol cannot be described by the mechanism showing the formation of C₂H₂O with the isomeric dihydro clinnamic aldehyde. Additionally the electron-impact-induced isomerization of allylic alcohols to ketones gives no plausible explanation for the experimental estimated ²H-part in the ion [C₇H₈]⁺˙. It is shown that the hydrogens of the side chain-C-atoms (1) and (2) participate mainly but not exclusively in the formation of the neutral part.