Calibrating SECCM measurements by means of a nanoelectrode ruler.The intrinsic oxygen reduction activity of PtNi catalyst nanoparticles

Scanning electrochemical cell microscopy(SECCM)is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle.This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images.Evidently,this becomes impossible for very small nanoparticles and hence,a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles.We show,that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined,the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles.     

Zum Einsatz von Verpresspfählen an Stelle von Verpressankern zur Rückverankerung von Spundwänden

Application of pressure-grouted piles instead of pressure-grouted anchors as bracings for sheet pile walls. Pressure-grouted piles are recently more and more often used instead of anchors as bracings for sheet pile walls. In Germany, the piles are mostly tested in the same way as anchors, i. e. according to DIN 4125. The load-deformation behaviour of pressure-grouted piles and anchors in sand during load testing and in the final state is investigated and compared. First, the different systems of both elements are described and the regulations according to the current standards are presented. Then calculation results obtained with the finite element method are presented. With respect to the final state, pressure-grouted piles show in usual load tests a significantly different, i. e. more favourable behaviour. The main reason for that is that in the load test, in contrast to the final state, anchor forces can be transferred to the soil inside the active sliding wedge. This effect is even enforced by a restraint between wall and soil due to the propping of the hydraulic jack for the test load against the wall. These effects must be considered in the evaluation of load test results with pressure-grouted piles.     

Nichtlineare Stabwerksstatik mit dem Weggrößenverfahren

Non‐linear Frame Analysis with the Displacement‐Method Modifications of the deformation based method are described which enable to analyse the non‐linear structural behaviour of reinforced concrete framed structures. The iterative calculation of the isolated members considers the end restraints from the rotations and displacements of the nodes. These deformations are determined iteratively from equilibrium conditions. The example uses mathematical methods for which standard functions are available in mathematic programs.     

Effects of ions on adenosine binding and enzyme activity of purified S-adenosylhomocysteine hydrolase from bovine kidney

The present investigation was undertaken to determine the effect of various ions on the characteristics of S-adenosylhomocysteine (SAH) hydrolase from bovine kidney. The binding sites of [3H]-adenosine to purified SAH hydrolase were not influenced by phosphate, magnesium, potassium, sodium, chloride or calcium ions at physiological cytosolic concentrations. To test whether NAD+ in the SAH hydrolase is essential for adenosine binding, we prepared the apoenzyme by removing NAD+ with ammonium sulfate. The resulting apoenzyme did not exhibit any [3H]-adenosine binding. Since the apoenzyme was enzymatically inactive, it is suggested that adenosine binds to the active site and not to an allosteric site of the intact enzyme. The kinetics of the hydrolysis and the synthesis of SAH catalyzed by the enzyme SAH hydrolase were measured in the presence and absence of phosphate and magnesium. Phosphate increased the Vmax for both synthesis and hydrolysis. However, only the affinity of adenosine for SAH synthesis was significantly enhanced from 10.1+/-1.3 microM to 5.4+/-0.5 microM by phosphate. This effect was already maximal at a phosphate concentration of 1 mM. All other tested ions were without effect on the enzyme activity. Our results show that phosphate at physiological concentrations shifts the thermodynamic equilibrium of SAH hydrolase in the direction of SAH synthesis. These findings imply that SAH-sensitive transmethylation reactions are inhibited during renal hypoxia when intracellular levels of phosphate, adenosine, and SAH are elevated.