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Abstract  

Thermal properties such as melting and crystallization are important aspects in understanding the morphology and its contribution to the physical properties of semicrystalline polymers, such as polypropylene. The inclusion of fillers, which are small particles dispersed in the continuous polymer phase, often complicates the predictability of these properties by acting as nucleating agents or defect origins. This paper discusses the creation and use of empirical models based on experimental data for predicting and optimizing the thermal properties of agricultural filler-polypropylene (AgFiller-PP) composites, including peak melting temperature (T m), peak crystallization temperature (T c) and percent of crystallinity (X c). Experiments were performed using differential scanning calorimetry (DSC) to gather data necessary for building appropriate prediction models. Finally, additional experiments were carried out to test the prediction results generated by the models.

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Periodica Mathematica Hungarica
Authors:
J. Fritz
,
T. Vicsek
, and
L. Simon
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Suspensions of a bioluminescent (luxAB) transformant of Listeria monocytogenes in pH 7.0 phosphate buffer were pressurised and the effect of the pressure treatment was monitored by plate counting. When the bacteria were suspended in NaCl- and nisin-free buffer the number of colony forming units (CFU) decreased by 3 and 6 log cycles after 300 MPA for 10 and 30 min, respectively. Supplementing the plating medium with 5% NaCl did not influence the colony forming capacity of non-pressurised cells, however, CFU of residual populations after respective treatments of 300 MPa for 10 and 30 min were reduced by a further 2 and 3.5 log cycles in case of salt containing plates. Nisin-addition to the plating medium caused less than one log unit decrease in the CFU of the non-pressurised population. However, the CFU of 10 min-pressurised sample was 4 log cycles less in the nisin-containing plates than in the nisin-free ones, whereas no colonies were formed in the nisin-containing plates even when 1 ml was inoculated from the originally 1010 CFU/ml population after 300 MPa for 30 min. The luciferase activities (bioluminescence intensities) decreased concomitant with the reduction of the viable cell counts, however, they were approx. 0.6-0.8 log units less in the presence of 5% NaCl in the pressurised suspension than those expected from the previously established linear correlation between the logarithmic light outputs and the logarithmic viable cell counts.

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Abstract  

The rate of thermal exchange reactions between carboxyl groups and14CO2 increases in the presence of catalytic amounts of alkali malonates. This catalytic effect can be utilized for preparative purposes also in the synthesis of11C-labelled aliphatic carboxylic acids from11CO2.

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A novel screening immunoassay for histamine was used for detection of histamine in different foodstuffs. The detection limit of this assay was 20 µg kg-1. The concentration of histamine varied between 182-982 µg kg-1 in sauerkraut, cheese and fish samples and 26-18433 µg l-1 in milk, sparkling wine and wines. The applied competitive enzyme immunoassay (ELISA) seemed a reliable technique for simple and rapid determination of histamine in food.

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A recombinant Bacillus subtilis strain containing a plasmid encoding a luxAB fusion, which gave bioluminescence upon addition of an exogenous long-chain aldehyde as substrate for the endogenous luciferase enzyme, was used as test organism. Its populations were treated with 300 MPa for 20 min, or 600 MPa for 20 min at around room temperature, and this treatment is foreseen as a quality-friendly, non-thermal pasteurisation of foods. Besides the estimation of viable cell counts, the extent of pressure-induced germination and post-process development were investigated by phase-contrast microscopy, turbidimetry and luminometry. Increased heat sensitivity of pressurized spore populations was observed both by viable cell counting during a linearly programmed elevation of temperature and a simultaneous differential scanning calorimetry. This was related to pressure-induced germination of spores, although a small fraction remained ungerminated. The luciferase pool built into the spores during their formation seemed to have withstood pressurization. Spore germination was accompanied by the emergence of bioluminescence which also indicated sensitively the characteristic changes of metabolic activity running parallel with the development of untreated cell populations and that of the survivors of the hydrostatic pressure treatments when the cells were incubated in a nutrient broth.

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The effects of the experimental conditions (sample size, heating rate, static and dynamic atmosphere) were studied on the value of the flash-ignition temperature (T i) obtained with a modified derivatograph able to measureT i simultaneously with the TG, DTG, DTA and T curves. The effects of various parameters are discussed and the optimum conditions determined.T i for bleached cotton fibre was found to be 270±1 °C.

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The glass transition of an irradiated, ultra-high molecular weight, linear polyethylene was investigated by means of the Perkin-Elmer DSC-2 differential scanning calorimeter. The experimental specific heat data were compared with those of the nonirradiated sample, obtained by DSC and adiabatic calorimetry.

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Periodica Mathematica Hungarica
Authors:
E. Puczylowski
,
T. Fényes
,
L. Simon
,
Zs. Harnos
, and
Z. Magyar
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Periodica Mathematica Hungarica
Authors:
L. Simon
,
H. Bernau
,
Gy. Molnárka
,
K. Győry
, and
V. Komornik
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