Yes (2090)
Number of found documents:
2090
Published from
to
Some Robust Approaches to Reducing the Complexity of Economic Data
Kalina, Jan
2023 - English
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.
Keywords:
dimensionality reduction; Big Data; variable selection; robustness; sparsity
Fulltext is available at external website.
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 - English
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.
Keywords:
linear regression; assumptions; non-standard situations; robustness; diagnostics
Fulltext is available at external website.
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 - English
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.
Keywords:
graph; graphon; graph fractional isomorphism
Available in digital repository of the ASCR
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 - English
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.
Keywords:
liquid-gas ejector; jet pump; design method
Available in digital repository of the ASCR
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, ...
Vývoj nástrojů pro minimalizaci rizik kontaminace ovzduší respirabilními azbestovými vlákny uvolňovanými lidskou činností z horninového prostředí – souhrnná výzkumná zpráva o průběhu a výsledcích řešení projektu
Vavro, Leona; Vavro, Martin; Daněk, T.; Kajzar, Vlastimil; Drozdová, J.; Raclavský, K.; Kubina, Lukáš
2023 - Czech
Souhrnná výzkumná zpráva přináší zhodnocení postupu a výsledků projektu SS01010257 - Vývoj nástrojů pro minimalizaci rizika kontaminace ovzduší respirabilními azbestovými vlákny uvolňovanými lidskou činností z horninového prostředí (AZROCK). Řešený projekt měl dva hlavní cíle. Prvním bylo vytvoření dvou metodických návodů, a to jednak pro odběr vzorků hornin a kameniva s možným obsahem přirozeně se vyskytujících azbestů a jednak pro následnou analýzu přítomnosti azbestových vláken v odebraných vzorcích. Dále si projekt stanovil za cíl tvorbu specializované mapy rizika výskytu azbestu v horninovém prostředí v České republice a internetového znalostního portálu azbestů. Podstatná část řešení projektu byla založena na odběru vzorků hornin a kameniva na téměř stovce vytipovaných lokalit po celé České republice a jejich následném vyhodnocení zvoleným a ověřeným souborem analytických metod. Podobné informace o výskytu azbestu v horninovém prostředí České republiky nebyly dosud zájemcům z řad odborné i laické veřejnosti k dispozici. The summary research report provides an evaluation of the procedure and results of the project SS01010257 - Development of tools to minimise the risks of air contamination by respirable asbestos fibres released from the rock environment by human activities (AZROCK). The solved project had two main objectives. The first one was the creation of two methodical instructions, both for the rock and aggregate sampling with a possible naturally occurring asbestos content and for the subsequent analysis of the presence of asbestos fibers in the samples taken. Furthermore, the project set itself the goal of creating: (1) a specialized map of the risk of asbestos occurrence in the rock environment in the Czech Republic and (2) a web knowledge portal of asbestos. A substantial part of the project solution was based on the collection of samples of rocks and aggregates at almost a hundred selected sites throughout the Czech Republic and their subsequent evaluation using a selected and verified set of analytical methods. Similar information on the occurrence of asbestos in the rock environment of the Czech Republic has not yet been available to interested professionals and the non-specialist public.
Keywords:
naturally occuring asbestos; rocks; aggregate; sampling; analysis; Czech Republic
Fulltext is available at external website.
Vývoj nástrojů pro minimalizaci rizik kontaminace ovzduší respirabilními azbestovými vlákny uvolňovanými lidskou činností z horninového prostředí – souhrnná výzkumná zpráva o průběhu a výsledcích řešení projektu
Souhrnná výzkumná zpráva přináší zhodnocení postupu a výsledků projektu SS01010257 - Vývoj nástrojů pro minimalizaci rizika kontaminace ovzduší respirabilními azbestovými vlákny uvolňovanými lidskou ...
Vhodné restaurátorské postupy pro zachování stop opracování kamene. Využití blízké fotogrammetrie k ohodnocení vhodnosti restaurátorských postupů
Cihla, Michal; Frommeltová, E.; Hodač, J.; Kovářová, K.; Pavelka, K.; Panáček, M.; Valach, Jaroslav
2023 - Czech
Tento památkový postup je výsledkem výzkumného projektu s názvem „Topografie povrchu kamene a její aplikace v oblasti restaurování kamenných prvků“ č. DG20P02OVV021, podpořeném Ministerstvem kultury ČR. Cílem památkového postupu bylo ověření vhodnosti a použitelnosti přesných měřičských metod za účelem zhodnocení míry restaurátorského zásahu v oblasti stop po opracování povrchu kamene. Nástrojem pro hodnocení změn topografie kamenných povrchů nesoucích stopy po opracování byla zvolena metoda blízké fotogrammetrie. This preservation procedure is the result of the research project entitled „Building stone surface topography and its application in the field of stone features restoration“ No.DG20P02OVV021, supported by the Ministry of Culture of the Czech Republic. The aim of the preservation procedure was to verify the suitability and applicability of precise measuring methods in order to assess the degree of restoration intervention in the area of traces of stone surface working. The method of close-range photogrammetry was chosen as a tool to evaluate the changes in the topography of stone surfaces bearing traces of working.
Keywords:
stone topography; photogrammetry; stonemason’s tools traces; restoration; conservation; stone; monuments; building stone
Fulltext is available at external website.
Vhodné restaurátorské postupy pro zachování stop opracování kamene. Využití blízké fotogrammetrie k ohodnocení vhodnosti restaurátorských postupů
Tento památkový postup je výsledkem výzkumného projektu s názvem „Topografie povrchu kamene a její aplikace v oblasti restaurování kamenných prvků“ č. DG20P02OVV021, podpořeném Ministerstvem kultury ...
Dynamics of a cantilever beam with piezoelectric sensor: Parameter identification
Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
2023 - English
The piezoelectric materials are electroactive materials often applied for real-time sensing or structural health monitoring, both important research topics in dynamics. Mathematical models of such structures have to allow also for the external electrical circuits and contain several material parameters that need to be identified from experiments. We present a model of a simple experiment involving dynamics of a cantilever beam with an attached piezoelectric sensor excited by a suddenly removed weight. The external circuit can be taken into account as having either a finite or infinite resistance. We also outline the parameter identification procedure based on automatic differentiation and present the experimental and numerical results.
Keywords:
finite element method; piezo-electricity; floating potential; dynamic simulation; parameter identification
Fulltext is available at external website.
Dynamics of a cantilever beam with piezoelectric sensor: Parameter identification
The piezoelectric materials are electroactive materials often applied for real-time sensing or structural health monitoring, both important research topics in dynamics. Mathematical models of such ...
Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting
Svárovský, Jiří; Parma, Slavomír; Štefan, Jan; Ciocanel, C.; Feigenbaum, H. P.; Marek, René; Klepač, Vilém; Plešek, Jiří
2023 - English
Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ratcheting, they often fail when validated with experimental data collected under a wide array of loading conditions. In this study, an experimental setup was developed and an autonomous testing procedure was used to experimentally analyze the evolution of the yield surface shape due to cyclic biaxial loading. Thin-walled tubular test specimens were made of 304L steel with a diameter of 40mm and underwent axial-torsional testing using the Instron 8852 system. The total axial strain was increased from 0 to 1% while the total shear strain underwent 5 cycles with the strain amplitude of 0.5% and the mean strain of 0.5%. Three yield surfaces were measured after the straining sequence was completed. Results showed strong directional distortional hardening and good agreement between the flow vectors and the normals to the yield surface, lending support to the associative flow rule.
Keywords:
yield surface distortion; strain hardening; multiaxial ratcheting; flow rule
Fulltext is available at external website.
Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting
Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ...
Numerical minimization of energy functionals in continuum mechanics using hp-FEM in MATLAB
Moskovka, Alexej; Frost, Miroslav; Valdman, Jan
2023 - English
Many processes in mechanics and thermodynamics can be formulated as a minimization of a particular energy functional. The finite element method can be used for an approximation of such functionals in a finite-dimensional subspace. Consequently, the numerical minimization methods (such as quasi-Newton and trust region) can be used to find a minimum of the functional. Vectorization techniques used for the evaluation of the energy together with the assembly of discrete energy gradient and Hessian sparsity are crucial for evaluation times. A particular model simulating the deformation of a Neo-Hookean solid body is solved in this contribution by minimizing the corresponding energy functional. We implement both P1 and rectangular hp-finite elements and compare their efficiency with respect to degrees of freedom and evaluation times.
Keywords:
hp-FEM; energy functionals; numerical minimization
Fulltext is available at external website.
Numerical minimization of energy functionals in continuum mechanics using hp-FEM in MATLAB
Many processes in mechanics and thermodynamics can be formulated as a minimization of a particular energy functional. The finite element method can be used for an approximation of such functionals in ...
Some Robust Approaches to Reducing the Complexity of Economic Data
Kalina, Jan
2023 - English
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.
Keywords:
dimensionality reduction; Big Data; variable selection; robustness; sparsity
Fulltext is available at external website.
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 ...
NRGL provides central access to information on grey literature produced in the Czech Republic in the fields of science, research and education. You can find more information about grey literature and NRGL at service web
Send your suggestions and comments to nusl@techlib.cz
Provider
Other bases