On the Theory of Rotary Mappings

Mathematical Notes -     

Some physical properties of ZnS crystals grown from the vapour phase

Wurtzite-type crystals with wide regions of high purity and good optical properties have been grown in a few hours by an improved flow method. Dislocations have been found to be mainly arranged inside isolated striation regions where a weak green fluorescence and phosphorescence has been observed. Under bending deformation the crystals show a plastic behaviour that is not directly correlated to the mean dislocation density of the samples. Rupture has been found at about 10³ kg/cm².The microwave method for the detection of crystal deflection has been suggested by Prof. A. Gozzini. His helpful advice and interest in this research has been deeply appreciated. Many thanks are also due to the Physical Institute of SAV in Prague, for the possibility to work on their crystals of ZnS. Finally we wish to thank Mr. Coli and Mr. Montanari for design and construction of the mechanical equipment and the furnace quartz assembly.     

The influence of pressure on the luminescence of zinc sulphide single crystals

Experiments were made which show that luminescence originated under the application of pressure on the single crystals of zinc sulphide. The calculated formula gives the same dependence of luminescence on the change of pressure dP/dt as in [1], [2].     

Aerosol radioactivity monitoring in Bratislava following the Chernobyl accident

The radiation situation in Bratislava following the Chernobyl accident is discussed. Measurement results of - and -radioactivity of aerosols are presented. The evolution of the activity ratios in air for some radionuclides is discussed. Their distribution indicates different transport and deposition properties for the volatile and nonvolatile fission products. The results are compared with long-term measurements of anthropogenic radionuclides released to the atmosphere by nuclear bomb tests.     

Radionuclide content in some building materials and their radon exhalation

The activity concentrations of natural radionuclides in sands, gravels, cements and in different kinds of concretes were measured by -spectrometric methods. The²²²Rn exhalation rate from concretes was measured by closed chamber method and the emanation coefficient was calculated. Both used methods are described in detail and obtained results are discussed from point of view of allowed hygienic limits.     

Low-level single and coincidence gamma-ray spectrometry

Analyses of anthropogenic and natural gamma-ray emitters in the environment require high sensitive detector systems operating in coincidence-anticoincidence modes. Thanks to an excellent energy resolution and a high efficiency, large volume HPGe detectors have been widely used in low-level gamma-ray spectrometry. In the present paper we discuss the characteristics of single and coincidence (HPGe-NaI(Tl)) arrangements suitable for analysis of environmental samples containing cascade gamma-ray emitters (e.g., ⁶⁰Co), positron emitters (e.g., ²²Na) and single gamma-ray emitters (e.g., ¹³⁷Cs). The detectors were placed in a large volume shields consisting of iron, lead and copper layers. The reduction of background for the single gamma-ray spectrometer is between 60 and 250, depending on the gamma-ray energy. As an improvement of the apparatus, low detection limits for analysis of ¹³⁷Cs (0.3 Bq·kg⁻¹) and ⁶⁰Co (0.1 Bq·kg⁻¹) in environmental samples, respectively, have been obtained.     

Synthesis,Properties, and Reactions of 5-Substituted Derivatives of 2,3-Diphenylquinoxaline [1]

Summary. Catalytic hydrogenation of 5-nitro-2,3-diphenylquinoxaline led to the corresponding amine which, in turn, afforded products of nucleophilic substitution on reaction with alkoxymethylene derivatives. Thermal cyclization of selected alkoxymethylene derivatives yielded substituted pyridoquinoxalines. The conditions for successful hydrolysis of ester, decarboxylation of the acid, following chlorination of pyridone and reductive removal of the chlorine atom from it to produce parental heterocycle 2,3-diphenyl-pyrido[2,3-f]quinoxaline were found. All of the tested products of the nucleophilic substitution showed no antibacterial activity.Dedicated to Prof. Dr. M. Uher on the occasion of his 65^th birthday     

On canonical almost geodesic mappings which preserve the weyl projective tensor

We study a partial case of canonical almost geodesic mappings of the first type of spaces with affine connection that preserve Weyl projective curvature tensor and certain other tensors. Main equations under consideration are reduced to a closed Cauchy system type in covariant derivatives. Therefore a general solution to these equations depends on a finite number of constants. We submit an example of above mappings between flat spaces. We establish that projective Euclidean and equiaffine spaces form closed classes of spaces with respect to these mappings.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.     

Intensitive dependence of luminescence and photoconductivity for the electron-electron,electron-exciton and exciton-exciton interactions

Analytical solutions of the equations of kinetics were found for stationary states at specific external conditions, especially for high excitation intensities. This allowed us to establish analytical expressions of the lux-lux and lux-ampere characteristics and use them in analyzing the type of recombination mechanism, which corresponds to certain dependence of luminescence or photoconductivity on the excitation intensity.