Circumstellar dust and variability of carbon stars

A sample of 35 variable carbon stars has been considered. The stellar temperatures, radii, absolute luminosities, masses, and mass loss rates have been estimated. Then the spherical circumstellar dust shells around the analysed stars are discussed and the differences in the infrared properties between semi-regular, irregular, and long-period variables are indicated.     

Zur Revision der GattungGloeocapsa Kützing (Cyanophyta)

Ohne Zusammenfassung Die vorliegende Arbeit entstand dank der Unterstützung der Alexander-von-Humboldt-Stiftung, Bad Godesberg.     

Experimental investigation of seismic behaviour of the ancient Protiron monument model

Throughout history, dry-stone masonry structures have been strengthened with different types of metal connectors in order to increase their resistance which enabled their survival, especially in the seismically active area. One such example is the ancient Protiron monument placed in the Peristyle square of the Diocletian's Palace in Split, Croatia. The Protiron was built at the turn of the 3rd century as a stone masonry structure with dowels embedded between its base, columns, capitals and broad gable. The stone blocks in the broad gable were connected by metal clamps during restoration at the beginning of the 20th century. In order to study the seismic performance of the strengthened stone masonry structures, an experimental investigation of seismic behaviour of a physical model of the Protiron was performed on the shaking table. The model was designed as a true replica model in a length scale of 1:4 and exposed to representative earthquake with increasing intensities up to collapse. The tests provided a clear insight into system behaviour, damage mechanism and failure under intensive seismic load, especially into the efficiency of connecting elements, which had a special role in increasing seismic resistance and protection of the structure from collapse. Additionally, this experiment provided valuable data for verification and calibration of numerical models for strengthened stone masonry structures.     

Correlations of natural radionuclides in sediment from Danube

The correlation between specific activities of some natural radionuclides (²³⁸U, ²²⁶Ra, ²³²Th, ⁴⁰K) measured in sediment taken from river bottom was studied. The sediment was taken from the Serbian part of the Danube River. Good correlation between some of the isotopes is observed, so that their specific activity ratios are spread over a lower range than specific activities themselves. This suggests that evaluation of specific activity ratios of some natural radionuclides could be a more sensitive method for the determination of increased levels of some of them than the straightforward analysis of specific activities.     

On Data Interpolation at Three Croatian Repeat Stations by Using the Spherical Elementary Currents Systems Method

A general mathematical tool for expanding vector systems on a sphere into basis functions, spherical elementary current system (SECS) method, was applied for separation of the geomagnetic field variations into external and internal parts, over a limited region of central and southeastern Europe. The registered variations at three Croatian repeat stations were compared to the variations estimated by the SECS method using the variations from the different sets of observatories. The results of the SECS method were also compared to a simple assumption that the variations at repeat station are equal to those at particular observatory. The relevance of this comparison was to get an insight about the possibility of using the SECS method for estimating the geomagnetic field variations over Croatia. The guidelines for the application of the SECS method for the purpose of reducing repeat station data were also given.     

Origin,organic geochemistry,and estimation of the generation potential of Neogene lacustrine sediments from the Valjevo-Mionica Basin,Serbia

This paper reports an investigation of 60 samples of lacustrine sedimentary rocks of Neogene age lying at depths of 0–400 m in the Valjevo-Mionica Basin, Serbia. The goal of the study was to determine the origin and type of primary organic matter (OM), the degree of thermal alteration, the generation potential of OM from the rocks of this basin, and conditions in the sedimentation environment during the formation of the rocks. The potential of OM of the rocks was estimated on the basis of the thermolysis of a representative sample after its preliminary debituminization.     

Environmental impact of blasting at Drenovac limestone quarry (Serbia)

In present paper, the blast-induced ground motion and its effect on the neighboring structures are analyzed at the limestone quarry "Drenovac" in central part of Serbia. Ground motion is examined by means of existing conventional predictors, with scaled distance as a main influential parameter, which gave satisfying prediction accuracy (R > 0.8), except in the case of Ambraseys–Hendron predictor. In the next step of the analysis, a feed-forward three-layer back-propagation neural network is developed, with three input units (total charge, maximum charge per delay and distance from explosive charge to monitoring point) and only one output unit (peak particle velocity). The network is tested for the cases with different number of hidden nodes. The obtained results indicate that the model with six hidden nodes gives reasonable predictive precision (R ≈ 0.9), but with much lower values of mean-squared error in comparison to conventional predictors. In order to predict the influence level to the neighboring buildings, recorded peak particle velocities and frequency values were evaluated according to United States Bureau of Mines, USSR standard, German DIN4150, Australian standard, Indian DMGS circular 7 and Chinese safety regulations for blasting. Using the best conventional predictor, the relationship between the allowable amount of explosive and distance from explosive charge is determined for every vibration standard. Furthermore, the effect of air-blast overpressure is analyzed according to domestic regulations, with construction of a blasting chart for the permissible amount of explosive as a function of distance, for the allowable value of air-blast overpressure (200 Pa). The performed analysis indicates only small number of recordings above the upper allowable limit according to DIN4150 and DMGS standard, while, for all other vibration codes the registered values of ground velocity are within the permissible limits. As for the air-blast overpressure, no damage is expected to occur.