Experiments on periodic and chaotic motions of a parametrically forced pendulum

An experimental study of periodic and chaotic type aperiodic motions of a parametrically harmonically excited pendulum is presented. It is shown that a characteristic route to chaos is the period-doubling cascade, which for the parametrically excited pendulum occurs with increasing driving amplitude and decreasing damping force, respectively. The coexistence of different periodic solutions as well as periodic and chaotic solutions is demonstrated and various transitions between them are studied. The pendulum is found to exhibit a transient chaotic behaviour in a wide range of driving force amplitudes. The transition from metastable chaos to sustained chaotic behaviour is investigated.     

Properties of Building and Plastic Materials in the THz Range

We present measurements of the frequency dependent refractive index and absorption coefficient of a variety of common building and plastic materials between 100 and 1000 GHz. Accurate knowledge of the material parameters is indispensable for the modeling of bound media propagation phenomena including single and multiple reflections, transmission, diffraction and scattering effects. These models are for example required for a reliable channel simulation to investigate signal propagation in future wireless communication systems operating with Gigabit data rates at frequencies above 100 GHz. Also, the measured material parameters can be used for the investigation and development of THz system components.     

Degradation and epimerization of ergot alkaloids after baking and in vitro digestion

The degradation and epimerization of ergot alkaloids (EAs) in rye flour were investigated after baking cookies and subsequently subjecting them to an in vitro digestion model. Different steps of digestion were analyzed using salivary, gastric, and duodenal juices. The degradation and bidirectional conversion of the toxicologically relevant (R)-epimers and the biologically inactive (S)-epimers for seven pairs of EAs were determined by a HPLC method coupled with fluorescence detection. Baking cookies resulted in degradation of EAs (2–30?%) and a shift in the epimeric ratio toward the (S)-epimer for all EAs. The applied digestion model led to a selective toxification of ergotamine and ergosine, two ergotamine-type EAs. The initial percentage of the toxic (R)-epimer in relation to the total toxin content was considerably increased after digestion of cookies. Ergotamine and ergosine increased from 32 to 51?% and 35 to 55?%, respectively. In contrast, EAs of the ergotoxine type (ergocornine, α- and β-ergocryptine, and ergocristine) showed an epimeric shift toward their biologically inactive (S)-epimers. Further experiments indicated that the selective epimerization of ergotamine EAs occurs in the duodenal juice only. These results demonstrate that toxification of EAs in the intestinal tract should be taken into consideration.     

Experimental Characterization of Premixed Flame Instabilities of a Model Gas Turbine Burner

In recent years, the NO _x emissions of heavy duty gas turbine burners have been significantly reduced by introducing premixed combustion. These highly premixed burners are known to be prone to combustion oscillations. In this paper, investigations of a single model gas turbine burner are reported focusing on thermo-acoustic instabilities and their interaction with the periodic fluctuations of the velocity and pressure. Phase-locked optical measurement techniques such as LDA and LIF gave insight into the mechanisms.Detailed investigations of a gas turbine combustor rig revealed that the combustor as well as the air plenum oscillate in Helmholtz modes. These instabilities could be attributed to the phase lag of the pressure oscillations between the air plenum and the combustor, which causes an acceleration and deceleration of the air flow through the burner and, therefore, alternating patterns of fuel rich and lean bubbles. When these bubbles reach the reaction zone, density fluctuations are generated which in turn lead to velocity fluctuations and, hence, keep up the pressure oscillations.With increasing the equivalence ratio strong combustion oscillations could be identified at the same frequency. Similarly as with weak oscillations, Helmholtz mode pressure fluctuations are present but the resulting velocity fluctuations in the combustor can be described as a pumping motion of the flow. By the velocity fluctuations the swirl stabilization of the flame is disturbed. At the same time, the oscillating pressure inside the combustor reaches its minimum value. Shortly after the flame expands again, the pressure increases inside the combustor. This phenomenon which is triggered by the pressure oscillations inside the air plenum seems to be the basic mechanism of the flame instability and leads to a significant increase of the pressure amplitudes.     

Strong interaction shifts and widths in light kaonic atoms

Energy shifts and line widths of X-ray transitions in kaonic atoms have been measured with an accuracy of about 10%. These data have been interpreted in terms of an optical potential. Whereas earlier approaches based on the free K⁻N scattering lengths fail to reproduce the data, a set of effective parameters consistant with all now available experiments could be derived.     

Strong interaction effects in antiprotonic atoms

Yields of the last observable X-ray transitions in antiprotonic atoms have been measured for groups of neighbouring elements. In sulphur a natural line width and an energy shift could be observed. These data are compared with calculations describing the p?-nucleus interaction in terms of an optical potential using the free p?-N scattering lengths.