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Number of results: 7
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Abstract

The Indian Cave Sandstone (Upper Pennsylvanian, Gzhelian) from the area of Peru, Nebraska, USA, has yielded numerous isolated chondrichthyan remains and among them teeth and dermal denticles of the Symmoriiformes Zangerl, 1981. Two tooth-based taxa were identified: a falcatid Denaea saltsmani Ginter and Hansen, 2010, and a new species of Stethacanthus Newberry, 1889, S. concavus sp. nov. In addition, there occur a few long, monocuspid tooth-like denticles, similar to those observed in Cobelodus Zangerl, 1973, probably representing the head cover or the spine-brush complex. A review of the available information on the fossil record of Symmoriiformes has revealed that the group existed from the Late Devonian (Famennian) till the end of the Middle Permian (Capitanian).
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Abstract

Rapid development of computing and visualisation systems has resulted in an unprecedented capability to display, in real time, realistic computer-generated worlds. Advanced techniques, including three-dimensional (3D) projection, supplemented by multi-channel surround sound, create immersive environments whose applications range from entertainment to military to scientific. One of the most advanced virtual reality systems are CAVE-type systems, in which the user is surrounded by projection screens. Knowledge of the screen material scattering properties, which depend on projection geometry and wavelength, is mandatory for proper design of these systems. In this paper this problem is addressed by introducing a scattering distribution function, creating a dedicated measurement setup and investigating the properties of selected materials used for rear projection screens. Based on the obtained results it can be concluded that the choice of the screen material has substantial impact on the performance of the system
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Abstract

At the end of 2018, when the Hučivá Cave (Hučivá diera, Rausch Keller) was explored in Tatranská Lomnica, profile deposits in rear areas of the cave were found disturbed by an amateur excavation. One stone artefact was first found in back-dirt clay-layer material at the excavation pit, later joined by four more specimens from the cleaned pit profile. The Typological analysis of the artefacts shows, that their closest parallels are found in inventories of the Magdalenian culture. Hučivá is the only cave in the whole Tatras with documented prehistoric settlement and the only Slovak cave with evidence of the Magdalenian culture. The discovery provides new information concerning subsistence strategies of late Pleistocene hunters in High Tatra Mountain landscapes. In light of this discovery, the possibility of seasonal movements along the northern slopes of this mountains range to the east and then south, through the mountain passes to the upper Spiš region should now be considered.
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Abstract

In the extra-thick coal seams and multi-layered hard roofs, the longwall hydraulic support yielding, coal face spalling, strong deformations of goaf-side entry, and severe ground pressure dynamic events typically occur at the longwall top coal caving longwall faces. Based on the Key strata theory an overburden caving model is proposed here to predict the multilayered hard strata behaviour. The proposed model together with the measured stress changes in coal seam and underground observations in Tongxin coal mine provides a new idea to analyse stress changes in coal and help to minimise rock bursts in the multi-layered hard rock ground. Using the proposed primary Key and the sub-Key strata units the model predicts the formation and instability of the overlying strata that leads to abrupt dynamic changes to the surrounding rock stress. The data obtained from the vertical stress monitoring in the 38 m wide coal pillar located adjacent to the longwall face indicates that the Key strata layers have a significant influence on ground behaviour. Sudden dynamically driven unloading of strata was caused by the first caving of the sub-Key strata while reloading of the vertical stress occurred when the goaf overhang of the sub-Key strata failed. Based on this findings several measures were recommended to minimise the undesirable dynamic occurrences including pre-split of the hard Key strata by blasting and using the energy consumption yielding reinforcement to support the damage prone gate road areas. Use of the numerical modelling simulations was suggested to improve the key theory accuracy.
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Abstract

The draw theory is the foundation for decreasing ore loss and dilution indices while extracting deposits from mines. Therefore, research on draw theory is of great significance to optimally guide the draw control and improve the economy efficiency of mines. The laboratory scaled physical draw experiments under inclined wall condition conducted showed that a new way was proposed to investigate the flow zone of granular materials. The flow zone was simply divided into two parts with respect to the demarcation point of the flow axis. Based on the stochastic medium draw theory, theoretical movement formulas were derived to define the gravity flow of fragmented rocks in these two parts. The ore body with 55° dip and 10 m width was taken as an example, the particle flow parameters were fitted, and the corresponding theoretical shape of the draw body was sketched based on the derived equation of draw-body shape. The comparison of experimental and theoretical shapes of the draw body confirmed that they coincided with each other; hence, the reliability of the derived equation of particle motion was validated.
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Abstract

The objective of this paper is a review of data on reconstruction of the Pleistocene palaeogeography (environment) and stratigraphy based on studies of karst sites in the Świętokrzyskie (Holy Cross) Mountains. Although the number of known Pleistocene karst sites in this region is small, the investigations of them have played a crucial role in a research of the Pleistocene. The study of the Kozi Grzbiet site provided the first evidences for new climatostratigraphy and classification of glaciations in Poland. The explanation of genesis of cryogenic calcite crystals discovered in Chelosiowa Jama-Jaskinia Jaworznicka cave system started a new direction of palaeoenvironmental reconstructions of the last glacial period. Kadzielnia palaeontological site was one of the first Early Pleistocene fossil assemblages in karst studied in Poland, whereas Raj cave provided abundant palaeontological and archaeological material from the Last Glacial. Other sites are of less scientific importance, however some of them can be used in education and popularisation of geosciences. Small number of already studied sites does not exclude discoveries of next sites of high scientific importance.
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Abstract

In recent years, many scientific and industrial centres in the world developed virtual reality systems or laboratories. At present, among the most advanced virtual reality systems are CAVE-type (Cave Automatic Virtual Environment) installations. Such systems usually consist of four, five, or six projection screens arranged in the form of a closed or hemi-closed space. The basic task of such systems is to ensure the effect of user “immersion” in the surrounding environment. The effect of user “immersion” into virtual reality in such systems is largely dependent on optical properties of the system, especially on quality of projection of three-dimensional images. In this paper, techniques of projection of three-dimensional (3D) images in CAVE-type virtual reality systems are analysed. The requirements of these techniques for such virtual reality systems are outlined. Based on the results of measurements performed in a unique CAVE-type virtual reality laboratory equipped with two different 3D projection techniques, named Immersive 3D Visualization Lab (I3DVL), that was recently opened at the Gdańsk University of Technology, the stereoscopic parameters and colour gamut of Infitec and Active Stereo stereoscopic projection techniques are examined and discussed. The obtained results enable to estimate the projection system quality for application in CAVE-type virtual reality installations.
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