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Abstract  

Dependence of counting efficiency of 1-methyl [2-14C]-imidazolidinone-2 adsorbed on the surface of various silica gels (different grain size and pore diameter) on scintillator (PT, PPO, butyl-PBD) concentration in three scintillation solvents was investigated by means of liquid scintillation spectrometry. It was established that the reason for deviations of the experimental points from the standard channel ratio curve is scintillation heterogeneity of the measured system. Proposition of an additional mechanism for excitation energy transport straight from silica gel globules to adsorbed molecules of the scintillator is discussed.

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Abstract  

By means of liquid scintillation spectrometry we investigated the counting efficiency of the samples containing toluene solution of scintillator (PPO, butyl-PBD, PT) and 1-methyl[2−14C]imidazolidinone-2 adsorbed on the silicagel, depending on concentration of scintillator, mass of radioactive compound, and mass of another nonactive compound introduced to samples as an impurity. For the sake of comparison the efficiency of counting homogeneous samples and the ones with Ba14CO3 deposit was determined. It was found, that the efficiency of detection of a radioactive compound adsorbed on the silicagel is conditioned by composition of adsorptive layer on the support surface.

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Abstract  

Thin magnetite films grown on cleaved MgO (100) substrates were studied by in-situ conversion electron Mössbauer spectroscopy (CEMS) in the temperature range of 80 K–300 K. The film growth was monitored by low energy electron diffraction revealing a perfect epitaxy in the whole thickness range from 430 nm down to 3 nm. CEMS measurements proved an ideal magnetite stoichiometry of the 430 nm thick film reflected both in the hyperfine pattern and in the Verwey transition. The thinner films showed strong deviation from the bulk properties, which was attributed to the modification of composition at the MgO/Fe3O4 interface, at which a magnesium rich phase is supposed based on CEM spectra. This phase, which was not observed previously, could be detected thanks to highly sensitive low-temperature measurements.

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Acta Biologica Hungarica
Authors: A. Waśko, Monika Kordowska-Wiater, M. Podleśny, Magdalena Polak-Berecka, Z. Targoński, and Agnieszka Kubik-Komar

The central composite design was developed to search for an optimal medium for the growth of Lactobacillus rhamnosus OXY. The effect of various media components, such as carbon sources, simple and complex nitrogen sources, mineral agents, and growth factors (vitamins B, amino acids) was examined. The first-order model based on Plackett-Burman design showed that glucose, sodium pyruvate, meat extract and mineral salts significantly influenced the growth of the examined bacteria. The second-order polynomial regression confirmed that maximum biomass production could be achieved by the combination of glucose (12.38 g/l), sodium pyruvate (3.15 g/l), meat extract (4.08 g/l), potassium phosphate (1.46 g/l), sodium acetate (3.65 g/l) and ammonium citrate (1.46 g/l).The validation of the predicted model carried out in bioreactor conditions confirmed the usefulness of the new medium for the culture of L. rhamnosus OXY in large scale. The optimal medium makes the culture of the probiotic bacterium L. rhamnosus OXY more cost effective.

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