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In this column Periodica Mathematica Hungarica publishes current research problems whose proposers believe them to be within the reach of existing methods. Manuscripts should preferably contain the background of the problem and all references known to the author. The length of the manuscripts should not exceed two double-space type-written pages.

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In this column Periodica Mathematica Hungarica publishes current research problems whose proposers believe them to be within reach of existing methods. Manuscripts should preferably contain the background of the problem and all references known to the author. The length of the manuscripts should not exceed two double-spaced type-written pages.

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In this column Periodica Mathematica Hungarica publishes current research problems whose proposers believe them to be within reach of existing methods. Manuscripts should preferably contain the background of the problem and all references known to the author. The length of the manuscripts should not exceed two double-spaced typewritten pages.

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Abstract  

This paper investigates closure properties possessed by certain classes of finite subdirect products of prime rings. If ℳ is a special class of prime rings then the class ℳ of all finite subdirect products of rings in ℳ is shown to be weakly special. A ring S is said to be a right tight extension [resp. tight extension] of a subring R if every nonzero right ideal [resp. right ideal and left ideal] of S meets R nontrivially. Every hereditary class of semiprime rings closed under tight extensions is weakly special. Each of the following conditions imposed on a semiprime ring yields a hereditary class closed under right tight extensions: ACC on right annihilators; finite right Goldie dimension; right Goldie. The class of all finite subdirect products of uniformly strongly prime rings is shown to be closed under tight extensions, answering a published question.

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Abstract  

The leak-rate of Ar through seals of liquid sodium pumps for sodium-cooled fast reactors is measured by thermal neutron activation analysis of oil and air samples taken from the cooling and lubrication systems of the seals. A method to calculate the leak-rate through a triple seal from the increase of the Ar concentrations is given.

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To study the thermal explosion of liquids a low pressure autoclave has been built. The first stage of a thermal explosion, the thermal runaway, has been studied. Evaluation of the temperature-time history results in kinetic data. Comparison with other thermal methods shows that the reliability of the method is better than with DTA.

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Abstract  

In the present study, we report on the thermal properties of a series of benzodiazepines. The heat of fusion varied between approximately 25 and 40 kJ mol–1, except for oxazepam and lorazepam where dimerization in the solid state increased the heat of fusion to 78.54(±0.37) and 77.03 (±0.84)kJ mol–1, respectively. Heating alprazolam at a low rate (0.5 K min–1) showed that polymorphs I and II are an enantiotropic pair with a solid-solid transition at 481.4 K It was shown that all benzodiazepines could be transformed to the glassy state by cooling fused samples, irrespective of the cooling rate. The size of the relaxation endotherm accompanying the glass transition increased by heating the glassy drugs at a higher rate through T g or by cooling the fused samples at a slower rate. The time dependence of the glass to liquid transition can be described to a good approximation as a first order transformation. The Gordon-Taylor equation was used to predict T g of a binary mixture of temazepam, diazepam or prazepam with polyHEMA. It was shown that the predictability was acceptable as long as the drug concentration was below 10%w/w; at higher concentration, specific drug-polymer interactions causing changes in free volume of the system could not be ignored.

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Abstract  

Thermal analysis was performed on the anti-HIV agent loviride in order to test its suitability to be processed using hot-melt extrusion. Temperature characteristic parameters of crystallization were determined to quantify the stability of amorphous loviride. The present study has shown that cooling and heating loviride at different rates influenced its thermal stability. At high cooling rates melted loviride did not crystallize during cooling, and formed a glass that recrystallized during reheating. Very low cooling rates resulted in significant decomposition of the drug. The glass transition temperature was found to increase as a function of increasing heating rates and the activation energy for the transition from the glassy to the super-cooled liquid state was relatively high, indicating good stability of the glass.

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