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  • Author or Editor: A. Müller x
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Abstract  

Bisphenol-A polycarbonate (BAPC) was crystallised by exposure to acetone vapours for a period of 9 h; it developed a 20% crystallinity according to WAXS measurements. The samples of semi-crystalline BAPC were then submitted to a series of thermal treatments including annealing, self-nucleation and subsequent isothermal crystallizations. The results showed that the polymer possesses a remarkable crystalline memory and a much faster recrystallization and reorganization capacity (lamellar thickening) than its very low thermal crystallization rate. This peculiar crystallization behaviour probably stems from its rigid backbone molecular structure.

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Abstract  

In this work the transfer behavior of long living radionuclides from the Thorium decay series (Ra-228, Th-228, Th-232) as well as of K-40 and Cs-137 is studied. In a small area of middle Europe (southeast Gemany) showing an increased Thorium content of soil the activity concentrations in samples of feed plants, farm animals, farm animal products, roe deer has been determined. The concentration ratios feed-to-animal tissue and to animal products are calculated indicating a significantly enhanced transfer from feed to roe deer tissues. Determinations of the activity concentrations in fish (carp), pig (tissues), egg, milk complete this examinations. Among all studied samples which are important for human nourishing eggs and carp cause the greatest exposure by ingestion.

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Abstract  

The uptake and the long term behavior of Cs-137, Cs-134 and K-40 in the annual tree rings of spruce were examined. The youngest tree rings which are most active in water transport have higher activity concentrations, of K-40 and of radiocesium than the older ones. The activity concentration of Cs-137 in a water transporting tree ring can be well described as a function of the activity concentration of K-40. Furthermore a depth profile of the soil was taken and gives information, about the depth distribution of radiocesium and K-40.

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Abstract  

The uptake and the radial distribution of naturally occurring radionuclides in the tree rings of a spruce tree were examined. The activity concentrations of Pb-210 are at a constant level of about 1,7 Bq/kg dry weight (dw) in older tree rings but decrease to younger ones. We suggest that Rn-222 dissolved in the soil water is taken up in significant amounts by the tree roots and decays to Pb-210 within the wood. The activity concentrations of Ra-226 of about 2,0 Bq/kg (dw) are nearly constant over all tree rings. Ra-228 however showed a significantly different behavior. Futhermore the activity concentrations of U-, Th- and Pu-isotopes were determined. A depth profile of the soil within the root zone of the spruce gives further informations.

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Besides dispersity and morphology, structural characteristics are of importance for the estimation of amorphous synthetic silicic acids with regard to their application. The present publication shows that it is possible to identify the different silicic acid types on the basis of thermoanalytical studies. The TG and DTA results provide information on the type and quantity of adsorbed or chemically bound water, and on the oxidative decomposition of the organic coating agent.

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Abstract  

A method has been developed that utilizes a special custom-made mixing device and HPLC micro liter syringe to perform mixing experiments of liquid systems directly in open measuring cells of differential scanning calorimeters. The present paper describes how to determine mixing enthalpies from time scans of the isothermal heat flux during an exothermal or endothermal process. Using ethylene glycol and the slightly volatile component water to calibrate the mixing calorimeter, the mixing enthalpy of the binary system poly(ethylene glycol) 400/water could be determined with sufficient precision compared to the results of measurements with a conventional flow calorimeter.

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Abstract  

A new analytical method using metallic silver (110mAg) as radioreagent is reported. A known amount of excess oxidant is applied to the reducing agent which is to be determined. After the reaction has taken place, the excess of the oxidizing agent is reacted with the neutron-activated silver whereby110mAg ions are released. The count rate of the solution is proportional to the excess of the oxidant, thus it is possible to determine the original content of the reducing agent in question. The proposed redox procedure based on back measurements has been applied to determinations of hydrogen peroxide, sodium oxalate, potassium ferrocyanide(II), uranium(IV), as well as hydroquinone and ethanol in the μg range. The method makes use of calibration curves; the standard deviation is ±2% on the average. Necessary heights of the normal potentials of the involved systems, favourable reaction conditions, and kineticsa are discussed.

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Due to the increasing importance of quantified results of dynamic calorimetric measurements, the influence of single experimental parameters has been studied by some authors. We found that these results can be represented correctly only in a complex form. According to this experience, the experimental parameters were changed on the basis of statistically planned experiments. The numerous measurements were carried out with samples of indium, 1,3-dinitrobenze and polyethylene prepared in different ways. The results were evaluated in a complex form. The evaluation of the experimental data revealed a significant influence of the substance properties and the experimental parameters.

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