Ultrasonic fatigue tests with stabilized amplitude and controlled temperature

An attachment for fatigue testing was developed, complementary to a commercially available ultrasonic generator with a power of 200 W. The fundamental improvements are: a control system which stabilizes the fatigue amplitude, and a programming attachment which supplies ultrasonic fatigue pulses in order to prevent undesirable temperature rises caused by internal friction. Similar attachments were developed for generators with powers of 400, 1 000 and 2 500 W. These improved fatigue testing machines permit investigations concerning the fatigue behaviour of metals with a remarkably high degree of damping.     

Solvent influence on photochemical isomerizations: Photophysics of DODCI

We have studied the photophysics of DODCI dissolved in a series of polar solvents. Through measurements of the temperature dependence of the photoisomer quantum yield, fluorescence lifetime and fluorescence quantum yields we clarify the kinetic mechanism for nonradiative decay. By measuring the isomerization rate as a function of temperature at constant viscosity we are able to separate the innuence of internal barriers and solvent viscous drag. The apparent activation energy observed in solutions is less than the sum of the internal and viscosity activation energies. This is shown to be consistent with the full Kramer's rate expression for diffusive barrier crossing. We also establish the temperature dependence of a second “direct” internal conversion process which does not lead to photoisomer formation and dominates the nonradiative decay of DODCI at low temperatures or in a rigid matrix.     

Bridging the gap between homogeneous and heterogeneous catalysis: ortho/para H(2) conversion, hydrogen isotope scrambling, and hydrogenation of olefins by Ir(CO)Cl(PPh(3))(2)

Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms.     

Derivative discontinuities in time-dependent density-functional theory

Based on the Runge-Gross theorem for ensembles we investigate the influence of particle-number-changes on the exchange-correlation potential in time-dependent density-functional theory. We show that the potential changes discontinuously when the particle number crosses an integer value. Real-time simulations of an atomic ionization process demonstrate that this discontinuity appears naturally in the theory of the time-dependent optimized effective potential. The importance of such a discontinuity for physical processes, even such ones in which the particle number is a constant, is discussed.     

Correlations and counting statistics of an atom laser

We demonstrate time-resolved counting of single atoms extracted from a weakly interacting Bose-Einstein condensate of 87Rb atoms. The atoms are detected with a high-finesse optical cavity and single atom transits are identified. An atom laser beam is formed by continuously output coupling atoms from the Bose-Einstein condensate. We investigate the full counting statistics of this beam and measure its second order correlation function g((2))(tau) in a Hanbury Brown-Twiss type experiment. For the monoenergetic atom laser we observe a constant correlation function g((2))(tau)=1.00 +/- 0.01 and an atom number distribution close to a Poissonian statistics. A pseudothermal atomic beam shows a bunching behavior and a Bose distributed counting statistics.     

Real-Time Detection of Polymerase Activity Using Supercritical Angle Fluorescence

We investigated the incorporation efficiencies of different fluorescently labelled dNTPs with polymerases by complementary strand synthesis. For this reason single stranded DNA was immobilized on a coverslip and the increase of fluorescence due to the synthesis of the corresponding strand with tagged dNTPs was detected with a supercritical angle fluorescence biosensor in real-time. By comparison of the observed signal intensities it was possible to conclude that the system Cy5-dCTP-Klenow (exonuclease free) fragment gives the best incorporation yield of the investigated enzymes and dNTPs.