Ano (2275)
Počet nalezených dokumentů:
2275
Publikováno od
do
Underground Spaces In Bosonožský Hájek Nature Reserve And Their Geoeducation Importance
Kirchner, Karel; Kuda, František; Baldík, V.; Kubalíková, Lucie
2023 - anglický
Bosonožský hájek Natural Reserve (Brno, South Moravia) is a very important site from the Earth Science point of view, however, its geodiversity values have been rather overlooked and omitted in the past (the object of legal protection is the occurrence of well-preserved forest ecosystems and endangered species). In the last decades, a series of field work and geophysical measurements has been carried out and the Earth Science phenomena have been identified and described here. These are represented by a dense network of gullies that developed in Pleistocene loess and that are both of natural and anthropogenic origin (some gullies probably developed along the old paths) and specific underground spaces (so called dugouts). Until now, the dugouts in South Moravia have been investigated mainly by archaeologists and those in Bosonožský hájek NR have not been described in detail yet. This brief contribution brings new information about three underground landforms and their possible relationship to the age and development of the gullies. The possibility of different interpretations of the origin of these specific landforms can be considered an opportunity in the field of Earth Science (geosciences) education and as an interesting complement of tourist and recreational activities on site.
Klíčová slova:
gully network; loess; dugouts; Earth Science education
Dokument je dostupný na externích webových stránkách.
Underground Spaces In Bosonožský Hájek Nature Reserve And Their Geoeducation Importance
Bosonožský hájek Natural Reserve (Brno, South Moravia) is a very important site from the Earth Science point of view, however, its geodiversity values have been rather overlooked and omitted in the ...
Interpolation with restrictions -- role of the boundary conditions and individual restrictions
Valášek, Jan; Sváček, P.
2023 - anglický
The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed in many applications like e.g. in aeroacoustics, here we are particularly interested in the numerical flow simulation of a gradual channel collapse connected with a~severe deterioration of the computational mesh quality. Since the classical Lagrangian projection from one mesh to another is a dissipative method not respecting conservation laws, a conservative interpolation method introducing constraints is described. The constraints have form of Lagrange multipliers enforcing conservation of desired flow quantities, like e.g. total fluid mass, flow kinetic energy or flow potential energy. Then the interpolation problem turns into an error minimization problem, such that the resulting quantities of proposed interpolation satisfy these physical properties while staying as close as possible to the results of Lagrangian interpolation in the L2 norm. The proposed interpolation scheme does not impose any restrictions on mesh generation process and it has a relatively low computational cost. The implementation details are discussed and test cases are shown.
Klíčová slova:
interpolation; Lagrange multiplier; Lagrange projection
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Interpolation with restrictions -- role of the boundary conditions and individual restrictions
The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed ...
Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
Matoušková, M.; Fraindová, K.; Bejčková, M.; Kliment, Z.; Vlach, V.; Vlček, Lukáš
2023 - anglický
The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing dissolved organic carbon (DOC) into surface water in headwater areas with peatbogs. DOC concentrations are analysed in relation to extreme rainfall-runoff (R-R) events and according to the hydrological preconditions of the basin. These preconditions are described using selected hydroclimatic variables (14 days before the R-R event). The source data comes from stations of the Faculty of Science, Charles University, and the Czech Hydrometeorological Institute. For the evaluation of relations and processes, the Principal component analysis (PCA), hysteresis loops or Pearson correlation coefficient was used. The lag time of DOCmax for Qmax, the dependence of DOCmax and groundwater levels were studied. The influence of flow rate on the decline and ascent phases of DOC\nconcentrations by hysteresis loops and the influence of the number of partial flow maximums on the amount of transported DOC during the R-R event was analysed. Our first results show that great influence on the dynamic of DOC concentration in surface water has the change in groundwater-levels in the peatbog and the outflow amount during the R-R event. The hydroclimatic preconditions of the basin have also a significant influence on the DOC release. Changes in concentrations during R-R events also occurred for other compounds that were studied additionally. Particularly significant was the increase in metals (mainly Fe, Al, Mn) and base cation (K) and decrease in nitrate nitrogen.
Klíčová slova:
natural organic matter; dissolved organic carbon; peatbog; surface water
Dokument je dostupný na externích webových stránkách.
Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing ...
Some Robust Approaches to Reducing the Complexity of Economic Data
Kalina, Jan
2023 - anglický
The recent advent of complex (and potentially big) data in economics requires modern and effective tools for their analysis including tools for reducing the dimensionality (complexity) of the given data. This paper starts with recalling the importance of Big Data in economics and with characterizing the main categories of dimension reduction techniques. While there have already been numerous techniques for dimensionality reduction available, this work is interested in methods that are robust to the presence of outlying measurements (outliers) in the economic data. Particularly, methods based on implicit weighting assigned to individual observations are developed in this paper. As the main contribution, this paper proposes three novel robust methods of dimension reduction. One method is a dimension reduction within a robust regularized linear regression, namely a sparse version of the least weighted squares estimator. The other two methods are robust versions of feature extraction methods popular in econometrics: robust principal component analysis and robust factor analysis.
Klíčová slova:
dimensionality reduction; Big Data; variable selection; robustness; sparsity
Dokument je dostupný na externích webových stránkách.
Some Robust Approaches to Reducing the Complexity of Economic Data
The recent advent of complex (and potentially big) data in economics requires modern and effective tools for their analysis including tools for reducing the dimensionality (complexity) of the given ...
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
Kalina, Jan
2023 - anglický
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions of common statistical methods for every statistical modeling task and the most habitually used (“vanilla”) versions may yield rather misleading results in nonstandard situations. Linear regression is considered here as the most fundamental econometric model. First, the analysis of a world tourism dataset is presented, where the number of international arrivals is modeled for 140 countries of the world as a response of 14 pillars (indicators) of the Travel and Tourism Competitiveness Index. Heteroscedasticity is clearly recognized in the dataset. However, the Aitken estimator, which would be the standard remedy in such a situation, is revealed here to be very inappropriate, regression quantiles represent a much more suitable solution here. The second illustration with artificial data reveals standard regression quantiles to be unsuitable for data contaminated by outlying values, their recently proposed robust version turns out to be much more appropriate. Both illustrations reveal that choosing suitable methods represent an important (and often difficult) part of the analysis of economic data.
Klíčová slova:
linear regression; assumptions; non-standard situations; robustness; diagnostics
Dokument je dostupný na externích webových stránkách.
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions ...
Fractionally Isomorphic Graphs and Graphons
Hladký, Jan; Hng, Eng Keat
2023 - anglický
Fractional isomorphism is a well-studied relaxation of graph isomorphism with a very rich theory. Grebík and Rocha [Combinatorica 42, pp 365–404 (2022)] developed a concept of fractional isomorphism for graphons and proved that it enjoys an analogous theory. In particular, they proved that if two sequences of graphs that are fractionally isomorphic converge to two graphons, then these graphons are fractionally isomorphism. Answering the main question from ibid, we prove the converse of the statement above: If we have two fractionally isomorphic graphons, then there exist sequences of graphs that are fractionally isomorphic converge and converge to these respective graphons. As an easy but convenient corollary of our methods, we get that every regular graphon can be approximated by regular graphs.
Klíčová slova:
graph; graphon; graph fractional isomorphism
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Fractionally Isomorphic Graphs and Graphons
Fractional isomorphism is a well-studied relaxation of graph isomorphism with a very rich theory. Grebík and Rocha [Combinatorica 42, pp 365–404 (2022)] developed a concept of fractional isomorphism ...
Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Gebouský, Ondřej; Haidl, Jan
2023 - anglický
Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, e.g., as sprayers. However, a complex and reliable method for LGE design was not available in the open literature until recently. This contribution follows up on our recent works about the hydraulic behavior of LGE with undisturbed and destabilized liquid jets. This paper aims to summarize the device’s complicated hydraulics and characterize its optimal design for three industrially relevant applications - (a) LGE as the vacuum pump, (b) LGE as the gas purification equipment, and (c) LGE as the gas distributor for bioreactors.
Klíčová slova:
liquid-gas ejector; jet pump; design method
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, ...
Ambient organic aerosol origin at rural background site in the Czech Republic
Lhotka, Radek
2023 - anglický
Atmospheric aerosols (AA) are ubiquitous particles in the atmosphere that influence the Earth’s climatic system, environmental interactions, and human health. Among AA, great interest is dedicated to organic aerosols (OA) since it can represent from 20 to 90% of total submicron mass. Source apportionment of OA at background sites is one of the important tasks of current air quality protection.
Klíčová slova:
organic aerosol; air quality protection; ural background site
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Ambient organic aerosol origin at rural background site in the Czech Republic
Atmospheric aerosols (AA) are ubiquitous particles in the atmosphere that influence the Earth’s climatic system, environmental interactions, and human health. Among AA, great interest is dedicated to ...
How can we best eliminate pharmaceuticals from wastewater?
Bourassi, Mahdi
2023 - anglický
Persistent pharmaceutical occurrence in different lakes and rivers usually originates from live stocks, agriculture, aquaculture, households, and hospitals. The presence of these compounds in the ecosystems leads to fatal consequences. Pharmaceuticals can threaten microorganisms in the environment, either causing its deterioration or allowing pathogens to gain resistance against antibiotics and medical treatments. These occurrences in the environment questions the ability of conventional treatment to remediate pharmaceutical wastewater.
Klíčová slova:
wastewater; pharmaceuticals; membrane separation
Plné texty jsou dostupné v digitálním repozitáři NUŠL
How can we best eliminate pharmaceuticals from wastewater?
Persistent pharmaceutical occurrence in different lakes and rivers usually originates from live stocks, agriculture, aquaculture, households, and hospitals. The presence of these compounds in the ...
Synthesis and cytotoxicity of fluorinated mannosamines
Krčil, Aleš
2023 - anglický
The aim of the project is to synthesise mono-, di- and trifluoroanalogs of N-acetylmannosamines. The cytotoxicity of the final products towards selected cancer cells will be determined. The key intermediates are the corresponding multiply fluorinated mannosazidethioglycosides prepared from deoxyfluorinated 1,6-anhydro-2-azidoβ-D-hexopyranose precursors by ring-opening reactions with phenyltrimethylsilyl sulfide.
Klíčová slova:
synthesis; cytotoxicity; fluorinated mannosamines
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Synthesis and cytotoxicity of fluorinated mannosamines
The aim of the project is to synthesise mono-, di- and trifluoroanalogs of N-acetylmannosamines. The cytotoxicity of the final products towards selected cancer cells will be determined. The key ...
NUŠL poskytuje centrální přístup k informacím o šedé literatuře vznikající v ČR v oblastech vědy, výzkumu a vzdělávání. Více informací o šedé literatuře a NUŠL najdete na webu služby.
Vaše náměty a připomínky posílejte na email nusl@techlib.cz
Provozovatel
Zahraniční báze