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Michal Kováč

Abstract

Thin-walled centrically compressed members with non-symmetrical or mono-symmetrical cross-sections can buckle in a torsional-flexural buckling mode. Vlasov developed a system of governing differential equations of the stability of such member cases. Solving these coupled equations in an analytic way is only possible in simple cases. Therefore, Goľdenvejzer introduced an approximate method for the solution of this system to calculate the critical axial force of torsional-flexural buckling. Moreover, this can also be used in cases of members with various boundary conditions in bending and torsion. This approximate method for the calculation of critical force has been adopted into norms. Nowadays, we can also solve governing differential equations by numerical methods, such as the finite element method (FEM). Therefore, in this paper, the results of the approximate method and the FEM were compared to each other, while considering the FEM as a reference method. This comparison shows any discrepancies of the approximate method. Attention was also paid to when and why discrepancies occur. The approximate method can be used in practice by considering some simplifications, which ensure safe results.

Open access

Marianna Kováčová, Nela Doláková and Michal Kováč

Miocene vegetation pattern and climate change in the northwestern Central Paratethys domain (Czech and Slovak Republic)

The case study area covers the slopes of the tectonically quiet European platform and foreland of the tectonically active Carpathian mountain chain (Carpathian Foredeep and Vienna Basin). Therefore the research on pollen spectra mirrors not only the evolution of landscape in two areas with different geodynamics, but also climatic changes in the Central Paratethys domain during the studied time interval. According to the pollen data, the Early to Middle Miocene vegetation reflects subtropical climate with very mild (negligible) cooling events during this period. This is indicated by common occurrence of thermophilous taxa in the whole sedimentary record. The Middle Miocene landscape evolution, conditioned by uplift of the Carpathian mountain chain and subsidence of adjacent lowlands, led to commencement of the altitudinal zonation. The terrestrial and aquatic ecosystems confirm a subtropical climate (Miocene Climatic Optimum, Mi3 event) with some possible long term changes in humidity. The Late Miocene paleogeographical changes, but also general climatic oscillations in the northwestern Central Paratethys realm, resulted in decrease of the number of thermophilous taxa during this time (change in latitudinal position of the vegetation cover). Variously high mountain relief of the uplifted mountain chains (altitudinal zonality) created ideal conditions for mixed mesophytic forests (to open woodland — open grassland type), still with presence of evergreen taxa. A subtropical climate with gradual transition to warm temperate climatic conditions is supposed on the basis of the reconstructed vegetation cover.

Open access

Tamás Csibri, Samuel Rybár, Katarína Šarinová, Michal Jamrich, Ľubomír Sliva and Michal Kováč

Abstract

The Blatné Depression located in the NW part of the Danube Basin represents the northernmost sub-basins of the Pannonian Basin System. Its subsidence is associated with oblique collision of the Central Western Carpathians with the European platform, followed by the back-arc basin rifting stage in the Pannonian domain. The conglomerates recognized in the Cífer-2 well document the latest Burdigalian–early Langhian deposition in fan delta lobes situated above the footwall and hanging wall of a WSW–ENE trending fault system, the activity of which preceded the opening of the late Langhian–Serravallian accommodation space with a NE–SW direction. The provenance area of the “Cífer conglomerate” was linked to the Tatric Super-unit complexes. Similar rocks crop out in the southern part of the Malé Karpaty Mts. and are also present in the pre-Cenozoic basement of the Danube Basin. Documented extensive erosion of the crystalline basement and its sedimentary cover lasted until the early/middle Miocene boundary. The “Cífer conglomerate” has distinct clast composition. The basal part consists of poorly sorted conglomerate with sub-angular clasts of metamorphic rocks. Toward the overlying strata, the clasts consist of poorly sorted conglomerates with sub-rounded to well-rounded carbonates and granitoids. The uppermost part consists of poorly sorted conglomerates with sub-rounded to rounded clasts of carbonate, granitoid and metamorphic rock. Within the studied samples a transition from clast to matrix supported conglomerates was observed.

Open access

Miroslav Mikolášek, Michal Nemec, Jaroslav Kováč, Ladislav Harmatha and Lukáš Minařík

Abstract

In this paper we present the utilization of capacitance and current-voltage diagnostic techniques to analyse silicon heterojunction solar cell structures properties, particularly focused on the inspection of the amorphous emitter and amorphous silicon/crystalline silicon hetero-interface. The capacitance characterization of investigated samples have revealed the need for improvement of the a-Si:H/c-Si heterointerface quality as a main direction to obtain superior output performance of heterojunction cells. In addition, current-voltage characterization emphasized importance for enhancement of the light management in the structure. The obtained results demonstrate that electrical and capacitance diagnostic techniques can represents important diagnostic tools in the process of optimization of solar cells.

Open access

Martin Slabej, Michal Grinč, Matúš Kováč, Martin Decký and Štefan Šedivý

Abstract

The Žilina airport was after almost 50 years of use measured by non-invasive methods including GPR and Profilograph GE in order to investigate the quality of the runway pavement at the chosen spots. Since it was just a pilot action, a sample of survey was carried out. The testing spots were placed where the geologic drill core J02 have been drilled out. The measurements performed by Profilograph GE were used to verify the quality of the pavement surface in term longitudinal unevenness by means of index IRI and C. The GPR survey was performed in 3D geometry, hence in the x- and y-direction. A horn type antenna with central frequency of 2 GHz was used on the test field in order to verify the thicknesses of pavement construction layers. Here, the result of a 3D survey is presented. The investigation confirms two sub-horizontal construction layers of the runway pavement. In some areas the GPR interpretation was not possible due to the signal attenuation. This significant signal attenuation is found mainly in the areas where the linear cracks are situated.

Open access

Martin Slabej, Michal Grinč, Peter Kotek, Matúš Kováč and Martin Decký

Abstract

Qualitative characteristics of pavement in wide range reflects the pavement serviceability, which is a summary of the characteristics of the pavement, providing a fast, smooth, economical and especially safe driving of motor-vehicles. The target factor of pavement serviceability and safety of roads represents the quality of their surface properties. In the framework of research activities performed in the Research Centre founded under the auspices of University of Žilina, individual parameters of pavement serviceability were monitored by pavement surface scanning. This paper describes the creation of a 3D - road surface model and its analysis and evaluation from the viewpoint of two pavement serviceability parameters - the rut depth and texture. Measurements were performed on an experimental pavement section used contemporary in an Accelerated Pavement Testing experiment. The long-term goal is to ascertain functions predicting degradation of these two pavement serviceability parameters.

Open access

Michal Kováč, Rastislav Synak, Klement Fordinál, Peter Joniak, Csaba Tóth, Rastislav Vojtko, Alexander Nagy, Ivan Baráth, Juraj Maglay and Jozef Minár

Late Miocene and Pliocene history of the Danube Basin: inferred from development of depositional systems and timing of sedimentary facies changes

The development of the northern Danube Basin (nDB) was closely related to the Late Miocene geodynamic evolution of the Pannonian Basin System. It started with a wide rifting which led to subsidence of several basin depocenters which were gradually filled during the Late Miocene and Early Pliocene. In the Late Pliocene the subsidence continued only in the basin's central part, while the northern marginal zone suffered inversion and the uplifted sedimentary fill began to be eroded. Individual stages of the basin development are well recorded in its sedimentary succession, where at least three great tectono-sedimentary cycles were documented. Firstly, a lacustrine cycle containing Lower, Middle and lowermost Upper Pannonian sediments (A-F Zones; sensu Papp 1951) deposited in the time span 11.6-8.9 Ma and is represented in the nDB in Slovakia by the Ivanka and Beladice Formations. In the Danube Basin of the southern part in Hungary, where the formations are defined by the appearance of sedimentary facies in time and space, the equivalents are: (1) the deep-water setting marls, clays and sandy turbidites of the Endrod and Szolnok Formations leading to the overlying strata deposits of the basin paleoslope or delta-slope represented by the Algyő Formation, and (2) the final shallow-water setting deposits of marshes, lagoons and a coastal and delta plain composed of clays, sands and coal seams, represented by the Újfalu Formation. The second tectono-sedimentary cycle was deposited in an alluvial environment and it comprises the Upper Pannonian (G and H Zones; sensu Papp 1951) and Lower Pliocene sediments dated 8.9-4.1? Ma. The cycle is represented in the nDB, by the Volkovce Formation and in the southern part by the Zagyva Formation in Hungary. The sedimentary environment is characterized by a wide range of facies from fluvial, deltaic and ephemeral lake to marshes. The third tectono-sedimentary cycle comprises the Upper Pliocene sediments. In Slovakia these are represented by the Kolárovo Formation dated 4.1-2.6 Ma. The formation contains material of weathering crust preserved in fissures of Mesozoic carbonates, diluvial deposits and sediments of the alluvial environment.

Open access

Michal Kováč, Jozef Hók, Jozef Minár, Rastislav Vojtko, Miroslav Bielik, Radovan Pipík, Miloš Rakús, Ján Kráľ, Martin Šujan and Silvia Králiková

Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance model

The development of the Turiec Basin and landscape evolution in its catchment has been reconstructed by methods of geological research (structural geology, sedimentology, paleoecology, and geochronological data) as well as by geophysics and geomorphology. The basin and its surrounding mountains were a subject of a mass balance study during periods of tectonic activity, accompanied by considerable altitudinal differentiation of relief and also during quiet periods, characterized by a development of planation surfaces in the mountains. The coarse clastic alluvial fans deposited beneath the offshore pelitic sediments document the rapid Middle Miocene uplift of mountains on the margin of the Turiec Basin. The Late Miocene finegrained sedimentation represents the main fill of this basin and its origin was associated with the formation of planation surfaces in the surrounding mountains. The rapid uplift of the western and northern parts of the catchment area during the latest Miocene and Early Pliocene times further generated the deposition of coarse-grained alluvial fans. The Late Pliocene basin inversion, due to uplift of the whole Western Carpathians mountain chain, was associated with the formation of the Early Quaternary pediment and ultimately with the formation of the Turiec river terrace systems.

Open access

Michal Kováč, Eva Halásová, Natália Hudáčková, Katarína Holcová, Matúš Hyžný, Michal Jamrich and Andrej Ruman

Abstract

Depositional sequences originating in semi-enclosed basins with endemic biota, partly or completely isolated from the open ocean, frequently do not allow biostratigraphic correlations with the standard geological time scale (GTS). The Miocene stages of the Central Paratethys represent regional chronostratigraphic units that were defined in type sections mostly on the basis of biostratigraphic criteria. The lack of accurate dating makes correlation within and between basins of this area and at global scales difficult. Although new geochronological estimates increasingly constrain the age of stage boundaries in the Paratethys, such estimates can be misleading if they do not account for diachronous boundaries between lithostratigraphic formations and for forward smearing of first appearances of index species (Signor-Lipps effect), and if they are extrapolated to whole basins. Here, we argue that (1) geochronological estimates of stage boundaries need to be based on sections with high completeness and high sediment accumulation rates, and (2) that the boundaries should preferentially correspond to conditions with sufficient marine connectivity between the Paratethys and the open ocean. The differences between the timing of origination of a given species in the source area and timing of its immigration to the Paratethys basins should be minimized during such intervals. Here, we draw attention to the definition of the Central Paratethys regional time scale, its modifications, and its present-day validity. We suggest that the regional time scale should be adjusted so that stage boundaries reflect local and regional geodynamic processes as well as the opening and closing of marine gateways. The role of eustatic sea level changes and geodynamic processes in determining the gateway formation needs to be rigorously evaluated with geochronological data and spatially-explicit biostratigraphic data so that their effects can be disentangled.

Open access

Jozef Hók, Michal Kováč, Ondrej Pelech, Ivana Pešková, Rastislav Vojtko and Silvia Králiková

Abstract

The tectonic evolution of the pre-Cenozoic basement, as well as the Cenozoic structures within the Danube Basin (DB) and its northern periphery are presented. The lowermost portion of the pre-Cenozoic basement is formed by the Tatricum Unit which was tectonically affected by the subduction of the Vahicum / Penninicum distal continental crust during the Turonian. Tectonically disintegrated Tatricum overlaid the post-Turonian to Lower Eocene sediments that are considered a part of the Vahicum wedge-top basin. These sediments are overthrust with the Fatricum and Hronicum cover nappes. The Danube Basin Transversal Fault (DBTF) oriented along a NW–SE course divided the pre-Neogene basement of the DB into two parts. The southwestern part of the DB pre-Neogene basement is eroded to the crystalline complexes while the Palaeogene and Mesozoic sediments are overlaid by the Neogene deposits on the northeastern side of the DBTF. The DBTF was activated as a dextral fault during the Late Oligocene – Earliest Miocene. During the Early Miocene (Karpatian – Early Badenian) it was active as a normal fault. In the Middle – Late Miocene the dominant tectonic regime with NW – SE oriented extension led to the disintegration of the elevated pre-Neogene basement under the simple and pure shear mechanisms into several NE – SW oriented horst and graben structures with successive subsidence generally from west to east. The extensional tectonics with the perpendicular NE – SW orientation of the Shmin persists in the Danube Basin from the ?Middle Pleistocene to the present.