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Search Results: 1 - 10 of 14074 matches for " Jan Hradecky "
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Bedload Transport and Morphological Effects of High-Magnitude Floods in Small Headwater Streams - Moravskoslezské Beskydy Mts. (Czech Republic)
Tomá Galia, Jan Hradecky
Journal of Hydrology and Hydromechanics , 2011, DOI: 10.2478/v10098-011-0020-x
Abstract: Bedload transport observed during a flood in May 2010 gave rise to several forms of accumulations in small headwater basins located in the Western Flysch Carpathian Mountains, Czech Republic. We have investigated critical conditions of incipient motion of the largest boulders deposited during a c. Q100 flood event (flood competence method). We have tested several formulas designed for high gradient streams in two small basins in the conditions of local mid-mountain relief. The results show that a flood of such a magnitude is able to transport almost all surface bed material and that bedload transport in steep headwater streams (A ≤ 1 km2) is probably less selective as for the grain size than that in lower gradient gravel-bed streams. The authors discuss the importance of local basin predispostion factors in order to determine critical conditions for the onset of bedload transport.
Introduction to the special volume "Subduction-related igneous activity in Central America - its nature, causes and consequences"
Hradecky P
Journal of Geosciences , 2011, DOI: 10.3190/jgeosci.089
The Cinotepeque Range of central El Salvador: Geology, magma origin, and volcanism
Rapprich V,Hradecky P
Bulletin of Geosciences , 2005, DOI: 10.3140/bull.geosci.2005.04.277
Abstract: The Cinotepeque Range is a geological block in NW El Salvador with a complicated volcanic history. Due to the absence of data concerning the geological basement, it remains unclear when volcanic activity started in this zone. The oldest rocks found in the Cinotepeque Range are rhyolitic basal ignimbrites produced from unknown sources. Volcanic activity then proceeded with the silicic pyroclastic products of calderas, the activity of which can be traced up to the Holocene. It is difficult to identify the exact sources of individual pumiceous deposits. Their potential candidates are the three calderas Ilopango Antiguo, Old Coatepeque, and Chilamatal. Later, extrusions of lava sheets of 'inferior' and 'superior' andesites, interrupted by the deposition of agglomeratic pyroclastic flows, called 'Rana', covered the majority of the landscape. The Rana pyroclastic flows were most probably produced from Texistepeque Caldera located between the towns of Santa Ana and Metapán. The youngest volcanism is represented in this area by monogenic volcanic cones. Source vents of these youngest volcanic products are situated mostly on faults that cut and displace all older volcanic rocks. Two different processes of magma origin occurred during the volcanic history of this part of El Salvador: a) during the first stage magma originated by flux melting at a subduction zone; b) during the next stage the decompressional melting in a back-arc environment occurred.
Spectrometric and Voltammetric Analysis of Urease – Nickel Nanoelectrode as an Electrochemical Sensor
Jaromir Hubalek,Jan Hradecky,Vojtech Adam,Olga Krystofova,Dalibor Huska,Michal Masarik,Libuse Trnkova,Ales Horna,Katerina Klosova,Martin Adamek,Josef Zehnalek,Rene Kizek
Sensors , 2007, DOI: 10.3390/s7071238
Abstract: Urease is the enzyme catalyzing the hydrolysis of urea into carbon dioxide andammonia. This enzyme is substrate-specific, which means that the enzyme catalyzes thehydrolysis of urea only. This feature is a basic diagnostic criterion used in thedetermination of many bacteria species. Most of the methods utilized for detection ofurease are based on analysis of its enzyme activity – the hydrolysis of urea. The aim of thiswork was to detect urease indirectly by spectrometric method and directly by voltammetricmethods. As spectrometric method we used is called indophenol assay. The sensitivity ofdetection itself is not sufficient to analyse the samples without pre-concentration steps.Therefore we utilized adsorptive transfer stripping technique coupled with differential pulse voltammetry to detect urease. The influence of accumulation time, pH of supporting electrolyte and concentration of urease on the enzyme peak height was investigated. Under the optimized experimental conditions (0.2 M acetate buffer pH 4.6 and accumulation time of 120 s) the detection limit of urease evaluated as 3 S/N was 200 ng/ml. The activity of urease enzyme depends on the presence of nickel. Thus the influence of nickel(II) ions on electrochemical response of the enzyme was studied. Based on the results obtained the interaction of nickel(II) ions and urease can be determined using electrochemical methods. Therefore we prepared Ni nanoelectrodes to measure urease. The Ni nanoelectrodes was analysed after the template dissolution by scanning electron microscopy. The results shown vertically aligned Ni nanopillars almost covered the electrode surface, whereas the defect places are minor and insignificant in comparison with total electrode surface. We were able to not only detect urease itself but also to distinguish its native and denatured form.
The volcano-tectonic evolution of the Miocene Santa Lucía Volcano, Boaco district, Nicaragua
Buriánek D,Hradecky P
Journal of Geosciences , 2011, DOI: 10.3190/jgeosci.085
Abstract: The present-day Santa Lucía caldera is an erosional relic of a Late Oligocene to Early Miocene stratoshield volcano located in the south-western part of the Chortis Block in Central Nicaragua. Six main lithological units were recognized: (Unit I) dacitic ignimbrite of Boaco type, which represents the basement of the Santa Lucía caldera; (Unit II) dacitic ignimbrite of Fonseca type, locally intercalated with epiclastic and dacitic lavas; (Unit III) “lower” andesite lavas; (Unit IV) blocky, lithic-rich pyroclastic flow deposits, (Unit V) “upper” andesite and basalt lavas, and (Unit VI) epiclastic rocks (lahar deposits). On the basis of field mapping, petrological and geochemical data, a new model for the evolution of the Santa Lucía Volcano is presented. The first stage consisted of a series of strong Sub-Plinian eruptions, which produced thick ignimbrite units. These events destroyed the pre-existing volcanic edifice. The second stage was dominated by large explosive eruptions producing mainly non-welded dacitic—andesitic ignimbrites. The next stage resulted in the formation of andesitic lava flows and minor tephra fall-out deposits, covered by voluminous basaltic lavas. Lahars probably triggered by volcanic and/or seismic events represent the final stage of volcanic activity. From the Miocene onwards, volcanic rocks became deeply weathered and locally eroded. Strongly weathered rocks are susceptible to landslides, and surficial modification by post-volcanic slope movements is observed on the slopes of the Santa Lucía Volcano. Identification of the lithological units and their comparison with wider Tertiary volcanic areas in Central Nicaragua will contribute to the knowledge of the regional volcanic stratigraphy and evolution.
Middle Ordovician at Praha - erveny vrch Hill (Barrandian area, Czech Republic)
Budil P,?Chlupá? I,Hradecky P
Bulletin of Geosciences , 2003, DOI: 10.3140/bull.geosci.2003.02.091
Abstract: A large temporary excavation in the Middle Ordovician in the NE part of the Barrandian at Praha-Vokovice ( erveny vrch Hill) was studied. Volcanic products forming the lower part of the exposed Ordovician sequence are represented mostly by basalts and basaltic tuffs. The lowermost parts of the árka Formation contain very rich graptolite and phyllocarid fauna, whilst benthic organisms are very rare. This faunal association contrasts with the younger 'Euorthisina-Placoparia Community' sensu Havlí ek and Vaněk (1990) and enables comparison with other localities in the lower part of the árka Formation in the Prague Basin.
Propagators weakly associated to a family of Hamiltonians and the adiabatic theorem for the Landau Hamiltonian with a time-dependent Aharonov-Bohm flux
J. Asch,I. Hradecky,P. Stovicek
Mathematics , 2005, DOI: 10.1063/1.1895865
Abstract: We study the dynamics of a quantum particle moving in a plane under the influence of a constant magnetic field and driven by a slowly time-dependent singular flux tube through a puncture. The known adiabatic results do not cover these models as the Hamiltonian has time dependent domain. We give a meaning to the propagator and prove an adiabatic theorem. To this end we introduce and develop the new notion of a propagator weakly associated to a time-dependent Hamiltonian.
Mass-to-Light Ratios of Groups and Clusters of Galaxies
V. Hradecky,C. Jones,R. H. Donnelly,S. G. Djorgovski,R. R. Gal,S. C. Odewahn
Physics , 2000, DOI: 10.1086/317158
Abstract: We constrain the mass-to-light ratios, gas mass fractions, baryon mass fractions and the ratios of total to luminous mass for a sample of eight nearby relaxed galaxy groups and clusters: A262, A426, A478, A1795, A2052, A2063, A2199 and MKW4s. We use ASCA spatially resolved spectroscopic X-ray observations and ROSAT PSPC images to constrain the total and gas masses of these clusters. To measure cluster luminosities we use galaxy catalogs resulting from the digitization and automated processing of the second generation Palomar Sky Survey plates calibrated with CCD images in the Gunn-Thuan g, r, and i bands. Under the assumption of hydrostatic equilibrium and spherical symmetry, we can measure the total masses of clusters from their intra-cluster gas temperature and density profiles. Spatially resolved ASCA spectra show that the gas temperature decreases with increasing distance from the center. By comparison, the assumption that the gas is isothermal results in an underestimate of the total mass at small radii, and an overestimate at large cluster radii. We have obtained luminosity functions for all clusters in our sample. After correcting for background and foreground galaxies, we estimate the total cluster luminosity using Schechter function fits to the galaxy catalogs. In the three lowest redshift clusters where we can sample to fainter absolute magnitudes, we have detected a flattening of the luminosity function at intermediate magnitudes and a rise at the faint end. These clusters were fit with a sum of two Schechter functions. The remaining clusters were well fit with a single Schechter function.
A Longitudinal Analysis of the Stability of Household Money Demand  [PDF]
Jan Tin
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.23046
Abstract: Past aggregate time-series studies, conducted under the assumption of a representative economic agent, frequently show that the demand for narrowly defined M1, especially non-interest-yielding demand deposit, is unstable during periods of financial innovations. Whether this is longitudinally the case among life-cycle savers is unclear. This study utilizes longitudinal data to take another look and find that volatility in the demand for non-interest-earning checking accounts in the mid and late 1990s is attributable solely to the portion held for the transactions motive. When the conventional Baumol-Tobin model is extended to include human capital and family formation variables representing the life-cycle motive, equilibrium money demand is a stable function of both economic and demographic variables.
A Spectral Method in Time for Initial-Value Problems  [PDF]
Jan Scheffel
American Journal of Computational Mathematics (AJCM) , 2012, DOI: 10.4236/ajcm.2012.23023
Abstract: A time-spectral method for solution of initial value partial differential equations is outlined. Multivariate Chebyshev series are used to represent all temporal, spatial and physical parameter domains in this generalized weighted residual method (GWRM). The approximate solutions obtained are thus analytical, finite order multivariate polynomials. The method avoids time step limitations. To determine the spectral coefficients, a system of algebraic equations is solved iteratively. A root solver, with excellent global convergence properties, has been developed. Accuracy and efficiency are controlled by the number of included Chebyshev modes and by use of temporal and spatial subdomains. As examples of advanced application, stability problems within ideal and resistive magnetohydrodynamics (MHD) are solved. To introduce the method, solutions to a stiff ordinary differential equation are demonstrated and discussed. Subsequently, the GWRM is applied to the Burger and forced wave equations. Comparisons with the explicit Lax-Wendroff and implicit Crank-Nicolson finite difference methods show that the method is accurate and efficient. Thus the method shows potential for advanced initial value problems in fluid mechanics and MHD.
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