Swelling and fractal heterogeneities in networks

In this paper we revisit old swelling data on polymer networks that have not been interpreted theoretically on a closed molecular basis. If the osmotic pressure of the swollen network is compared to the osmotic pressure of the corresponding uncrosslinked solution unsolved problems appear, when the relative osmotic pressure is plotted against the degree of swelling, i.e. the deformation due to swelling. A significant maximum appears which cannot be explained by any of the recently derived elastic models, such as junction constraint or other entanglement models. It is suggested in this paper that the maximum is a consequence of structural heterogeneities of fractal nature. If such fractal heterogeneities are assumed a strong maximum in the relative osmotic pressure can be reproduced. The physical reason is the different thermodynamic behavior of uncrosslinked linear chains and crosslinked self-similar (non-linear) polymers. The conclusion is supported by numerical (Monte Carlo) simulations.     

Algebraic construction of a Nambu bracket for the two-dimensional vorticity equation

So far fluid mechanical Nambu brackets have mainly been given on an intuitive basis. Alternatively an algorithmic construction of such a bracket for the two-dimensional vorticity equation is presented here. Starting from the Lie-Poisson form and its algebraic properties it is shown how the Nambu representation can be explicitly constructed as the continuum limit from the structure preserving Zeitlin discretization.     

Laser drilling of stainless steel with nanosecond double-pulse

Nanosecond double-pulse laser drilling is reported in this paper. The double-pulse herein represents two closely conjoint pulses with 21 ns pulse duration and about 52 ns interpulse separation, which are acquired by temporal pulse shaping. Percussion drilling with such double-pulse is performed in stainless steel samples with different laser fluences, sample's thickness, repetition rates and ambient pressures. The experimental results show that the drilling rates of double-pulse drilling are more than one order of magnitude higher than that of conventional single-pulse drilling in air. Differences in the processing results between single-pulse and double-pulse with various processing parameters are investigated. In addition the ablation mechanisms of the double-pulse drilling are discussed.     

Powder dilution as a new method of elimination of interelement effects in energy-dispersive X-ray fluorescence analysis

Summary If the concentration of elements with Z>22 (Ti) is to be determined in mineral samples and if the concentration of any of these elements is greater than 1%, the sample is diluted by grinding it together with an appropriate amount of quartz powder in an agate mortar mill. The diluted sample is measured in powdered form in a spectro-cup at practically infinite thickness by energy-dispersive X-ray fluorescence; the counting rates are corrected by means of the Compton scattering peak and evaluated by use of calibration curves obtained by measuring standards on the basis of silica gel. The applicability of this method is established by measuring the concentrations of 12 elements with Z>22 in 14 mineral samples of varying composition.We thank the Bundesministerium für Forschung und Technologie for financial support and the Uranerzbergbau GmbH, Bonn, for supplying the mineral samples.     

Das anodische Verhalten von Acetationen in nichtwäßriger Lösung an einer rotierenden Platinscheibenelektrode

Acetate ions are irreversibly oxidized in nonaqueous solutions. The electron transfer reaction is believed to be the rate determining step. Increasing addition of acetic acid which itself is not oxidized shifts the half wave potential towards more positive values. This change is interpreted in terms of the formation of a 1:1 complex between acetate ions and acetic acid. This shift allows to obtain a polarographic wave forDMF in acetic acid-acetate system although the acetate ions on their part give a polarographic wave inDMF.     

Kupfer

Ohne Zusammenfassung     

Suche nach Strahlungsprozessen zweiter Ordnung beim Zerfall von Ag109m

The decay of an excited state by the emission of twoγ-quanta (γ γ-transitions) or two conversion electrons (e e-transitions) or oneγ-quantum and one conversion electron (γ e-transitions) is expected as a second order radiation process. The decay of Ag^109m was examined for such events using a special arrangement of two NaJ-scintillation counters in coincidence. The energies of coincident quanta were displayed on the two axes of an “X-Y”-Oscilloscope respectively. For the ratio ofγ γ-transitions to one-quantum transitions an upper limit of\(\frac{{W_{\gamma \gamma } }}{{W_\gamma }} \leqq 1,9 \cdot 10^{ - 5} \) was obtained. Furthermore theγ-spectrum in coincidence withK X-rays was studied. From these measurementse e- andγ e-transition rates can be calculated for the case ofK shell conversion. The results obtained are:

$$\frac{{W_{^e K^e K} }}{{W_\gamma }} = \left( {8,1_{ - 1,7}^{ + 0,6} } \right) \cdot 10^{ - 3} and\frac{{W_{\gamma ^e K} }}{{W_\gamma }}< 1,5 \cdot 10^{ - 3} .$$