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130 results on '"Sebek, Ondrej"'

2. δ26Mg, δ44Ca and 87Sr/86Sr isotope ratios constrain Mg and Ca input–output mass balances in a heavily acidified headwater catchment

Author

Novak, Martin, Veselovsky, Frantisek, Hruška, Jakub, Holmden, Chris, Andronikov, Alexandre V., Erban Kochergina, Yulia V., Kachlik, Vaclav, Stepanova, Marketa, Pour, Ondrej, Sebek, Ondrej, Prechova, Eva, Komarek, Arnost, Curik, Jan, Laufek, Frantisek, Andronikova, Irina E., Fottova, Daniela, Holeckova, Pavla, and Paces, Tomas

Published
2024
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3. Sizeable net export of base cations from a Carpathian flysch catchment indicates their geogenic origin while the 26Mg/24Mg, 44Ca/40Ca and 87Sr/86Sr isotope ratios in runoff are indistinguishable from atmospheric input

Author

Novak, Martin, Kochergina, Yulia V. Erban, Andronikov, Alexandre V., Holmden, Chris, Veselovsky, Frantisek, Kachlik, Vaclav, Hruška, Jakub, Laufek, Frantisek, Paces, Tomas, Komarek, Arnost, Sebek, Ondrej, Stepanova, Marketa, Curik, Jan, Prechova, Eva, Fottova, Daniela, and Andronikova, Irina E.

Published
2024
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4. Mg, Ca and Sr isotope dynamics in a small forested catchment underlain by paragneiss: The role of geogenic, atmospheric, and biogenic sources of base cations

Author

Novak, Martin, Holmden, Chris, Andronikov, Alexandre V., Erban Kochergina, Yulia V., Kirchner, James W., Paces, Tomas, Kachlik, Vaclav, Veselovsky, Frantisek, Hruška, Jakub, Laufek, Frantisek, Koubova, Magdalena, Stepanova, Marketa, Prechova, Eva, Sebek, Ondrej, Curik, Jan, Tesar, Miroslav, Fottova, Daniela, Andronikova, Irina E., and Komarek, Arnost

Published
2024
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5. Imputation of missing sub-hourly precipitation data in a large sensor network: a machine learning approach

Author

Chivers, Benedict Delahaye, Wallbank, John, Cole, Steven J., Sebek, Ondrej, Stanley, Simon, Fry, Matthew, and Leontidis, Georgios

Subjects
Computer Science - Machine Learning, Statistics - Applications, Statistics - Machine Learning
Abstract

Precipitation data collected at sub-hourly resolution represents specific challenges for missing data recovery by being largely stochastic in nature and highly unbalanced in the duration of rain vs non-rain. Here we present a two-step analysis utilising current machine learning techniques for imputing precipitation data sampled at 30-minute intervals by devolving the task into (a) the classification of rain or non-rain samples, and (b) regressing the absolute values of predicted rain samples. Investigating 37 weather stations in the UK, this machine learning process produces more accurate predictions for recovering precipitation data than an established surface fitting technique utilising neighbouring rain gauges. Increasing available features for the training of machine learning algorithms increases performance with the integration of weather data at the target site with externally sourced rain gauges providing the highest performance. This method informs machine learning models by utilising information in concurrently collected environmental data to make accurate predictions of missing rain data. Capturing complex non-linear relationships from weakly correlated variables is critical for data recovery at sub-hourly resolutions. Such pipelines for data recovery can be developed and deployed for highly automated and near instantaneous imputation of missing values in ongoing datasets at high temporal resolutions., Comment: 24 pages, 7 figures, 5 tables

Published
2020
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7. Winter-time pollution in Central European cities shifts the 208Pb/207Pb isotope ratio of atmospheric PM2.5 to higher values: Implications for lead source apportionment

Author

Martinková, Eva, Kochergina, Yulia V.Erban, Šebek, Ondřej, Seibert, Radim, Chrastný, Vladislav, Novák, Martin, Štěpánová, Markéta, Čuřík, Jan, Pacherová, Petra, Přechová, Eva, Veselovský, František, Volná, Vladimíra, Hladký, Daniel, Petrash, Daniel A., and Komárek, Arnošt

Published
2023
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9. Spatial and temporal trends in δ66Zn and 206Pb/207Pb isotope ratios along a rural transect downwind from the Upper Silesian industrial area: Role of legacy vs. present-day pollution

Author

Prechova, Eva, Sebek, Ondrej, Novak, Martin, Andronikov, Alexandre V., Strnad, Ladislav, Chrastny, Vladislav, Cabala, Jerzy, Stepanova, Marketa, Pasava, Jan, Martinkova, Eva, Pacherova, Petra, Blaha, Vladimir, Curik, Jan, Veselovsky, Frantisek, and Vitkova, Hyacinta

Published
2023
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11. Chromium isotope systematics in three mantle-derived domains of Central European Variscides: Relationship between δ53Cr values and progressive weathering of serpentinized ultramafic rocks

Author

Novak, Martin, Andronikov, Alexandre V., Sebek, Ondrej, Kotkova, Jana, Erban Kochergina, Yulia V., Stepanova, Marketa, Strnad, Ladislav, Kram, Pavel, Farkas, Juraj, Veselovsky, Frantisek, Stedra, Veronika, Curik, Jan, Chrastny, Vladislav, Prechova, Eva, and Houskova, Marie

Published
2022
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12. δ26Mg, δ44Ca and 87Sr/86Sr isotope ratios constrain Mg and Ca input–output mass balances in a heavily acidified headwater catchment.

Author

Novak, Martin, Veselovsky, Frantisek, Hruška, Jakub, Holmden, Chris, Andronikov, Alexandre V., Erban Kochergina, Yulia V., Kachlik, Vaclav, Stepanova, Marketa, Pour, Ondrej, Sebek, Ondrej, Prechova, Eva, Komarek, Arnost, Curik, Jan, Laufek, Frantisek, Andronikova, Irina E., Fottova, Daniela, Holeckova, Pavla, and Paces, Tomas

Subjects
MAGNESIUM isotopes, CALCIUM isotopes, COAL-fired power plants, STRONTIUM isotopes, EARTH sciences, THROUGHFALL
Abstract

A Central European catchment underlain by base-poor orthogneiss was studied using mass budgets and Mg–Ca–Sr isotope systematics. For 50 years, the catchment received large amounts of partly soluble dust from a nearby cluster of coal-burning power plants, while suffering from acid rain and severe spruce die-back. Our objective was to investigate to what extent anthropogenic dust contributes to Mg and Ca in runoff and to identify fractionations affecting Mg and Ca isotope composition of 13 ecosystem pools and fluxes. We hypothesized that if Mg and Ca runoff fluxes were significantly larger than their atmospheric inputs, Mg and Ca isotope ratios in runoff would converge to those of bedrock Mg and Ca. This relationship could be obscured by isotope fractionations. Strontium characterized by negligible isotope fractionations served as a Ca proxy. There was a strong positive correlation between Mg and Ca fluxes via spruce throughfall and catchment runoff. Monitoring of rainfall, canopy throughfall and runoff fluxes revealed a 20-, 15- and 15-fold excess of Mg, Ca and Sr in runoff, respectively, compared to atmospheric deposition fluxes. This sizeable excess per se would indicate predominance of geogenic base cations in runoff. The behavior of Mg and Ca isotopes was de-coupled. Petrographic study indicated that 92% of bedrock Mg was bound to easily dissolving biotite, 97% Ca was present in plagioclase, and nearly all Sr was in orthoclase. While Mg isotope ratios in bedrock and runoff were indistinguishable, corroborating predominantly geogenic Mg in runoff, Ca and Sr isotope ratios in bedrock and runoff were significantly different, consistent with a non-negligible contribution of atmospheric Ca and Sr to runoff. Previous study of sites underlain by felsic rocks indicated that the δ44Ca value of apatite was often higher than the δ44Ca value of plagioclase. Should weathering of apatite and/or plagioclase preferentially release Ca that is isotopically heavier than bulk rock, the geogenic Ca source at JEZ would converge to the mean δ44Ca value of runoff. Calcium isotope data would then become more consistent with a major role of geogenic Ca in JEZ runoff indicated by mass balance data. [ABSTRACT FROM AUTHOR]

Published
2024
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14. Requirements for Information Modelling in Manufacturing

Author

Jirkovský, Václav, Obitko, Marek, Šebek, Ondřej, Kadera, Petr, Kacprzyk, Janusz, Series Editor, Pal, Nikhil R., Advisory Editor, Bello Perez, Rafael, Advisory Editor, Corchado, Emilio S., Advisory Editor, Hagras, Hani, Advisory Editor, Kóczy, László T., Advisory Editor, Kreinovich, Vladik, Advisory Editor, Lin, Chin-Teng, Advisory Editor, Lu, Jie, Advisory Editor, Melin, Patricia, Advisory Editor, Nedjah, Nadia, Advisory Editor, Nguyen, Ngoc Thanh, Advisory Editor, Wang, Jun, Advisory Editor, Paralič, Ján, editor, Sinčák, Peter, editor, Hartono, Pitoyo, editor, and Mařík, Vladimír, editor

Published
2021
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16. Semi-automatic Tool for Ontology Learning Tasks

Author

Šebek, Ondřej, Jirkovský, Václav, Rychtyckyj, Nestor, Kadera, Petr, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Woeginger, Gerhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Mařík, Vladimír, editor, Kadera, Petr, editor, Rzevski, George, editor, Zoitl, Alois, editor, Anderst-Kotsis, Gabriele, editor, Tjoa, A Min, editor, and Khalil, Ismail, editor

Published
2019
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17. Comparison of δ53CrCr(VI) values of contaminated groundwater at two industrial sites in the eastern U.S. with contrasting availability of reducing agents

Author

Novak, Martin, Sebek, Ondrej, Chrastny, Vladislav, Hellerich, Lucas A., Andronikov, Alexandre, Martinkova, Eva, Farkas, Juraj, Pacherova, Petra, Curik, Jan, Stepanova, Marketa, Prechova, Eva, Houskova, Marie, Zoulkova, Vera, Veselovsky, František, Svobodova, Irena, Janotova, Petra, and Komarek, Arnost

Published
2018
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21. Sizeable net export of base cations from a Carpathian flysch catchment indicates their geogenic origin while the 26Mg/24Mg, 44Ca/40Ca and 87Sr/86Sr isotope ratios in runoff are indistinguishable from atmospheric input

Author

Novak, Martin, Kochergina, Yulia V. Erban, Andronikov, Alexandre V., Holmden, Chris, Veselovsky, Frantisek, Kachlik, Vaclav, Hruška, Jakub, Laufek, Frantisek, Paces, Tomas, Komarek, Arnost, Sebek, Ondrej, Stepanova, Marketa, Curik, Jan, Prechova, Eva, Fottova, Daniela, and Andronikova, Irina E.

Subjects
FLYSCH, RUNOFF, ISOTOPES, FOREST health, BEDROCK, BARK beetles
Abstract

Nutrient imbalances may negatively affect the health status of forests exposed to multiple stress factors, including drought and bark beetle calamities. We studied the origin of base cations in runoff from a small Carpathian catchment underlain by base-poor flysch turbidites using magnesium (Mg), calcium (Ca) and strontium (Sr) isotope composition of 10 ecosystem compartments. Our objective was to constrain conclusions drawn from long-term hydrochemical monitoring of inputs and outputs. Annual export of Mg, Ca and Sr exceeds 5-to-15 times their atmospheric input. Mass budgets per se thus indicate sizeable net leaching of Mg, Ca and Sr from bedrock sandstones and claystones. Surprisingly, δ26Mg, δ44Ca and 87Sr/86Sr isotope ratios of runoff were practically identical to those of atmospheric deposition and soil water but significantly different from bedrock isotope ratios. We did not find any carbonates in the studied area as a hypothetical, easily dissolvable source of base cations whose isotope composition might corroborate the predominance of geogenic base cations in the runoff. Marine carbonates typically have lower δ26 Mg and 87Sr/86Sr ratios, and silicate sediments often have higher δ26Mg and 87Sr/86Sr ratios than runoff at the study site. Mixing of these two sources, if confirmed, could reconcile the flux and isotope data. [ABSTRACT FROM AUTHOR]

Published
2024
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49. Catchment Runoff in Industrial Areas Exports Legacy Pollutant Zinc from the Topsoil Rather than Geogenic Zn

Author

Andronikov, Alexandre V., primary, Novak, Martin, additional, Oulehle, Filip, additional, Chrastny, Vladislav, additional, Sebek, Ondrej, additional, Andronikova, Irina E., additional, Stepanova, Marketa, additional, Sipkova, Adela, additional, Hruska, Jakub, additional, Myska, Oldrich, additional, Chuman, Tomas, additional, Veselovsky, Frantisek, additional, Curik, Jan, additional, Prechova, Eva, additional, and Komarek, Arnost, additional

Published
2021
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