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A polarizable reference electrode
Mareček, Vladimír
2023 - English
New concept of a reference electrode for electrochemical systems resolves a problem of a poor \npotential stability of refence electrodes based on the distribution of a strongly \nhydrophobic common cation between two immiscible electrolyte solutions (TTTES). The use of a \npolarizable metal electrode instead of a classical reference electrode is demonstrated in \n a modified conventional four-electrode cell with TTTES. A simple battery operated potentiostat \ncontrols the working electrode potential in a three-electrode configuration. The working metal \nelectrode then serves as a polarizable reference organic solvent electrode in a four-electrode \nsystem for the polarization of the water/organic solvent interface.\n\n
Keywords:
reference electrode; liquid/liquid interface; chloride extraction
Available on request at various institutes of the ASCR
A polarizable reference electrode
New concept of a reference electrode for electrochemical systems resolves a problem of a poor \npotential stability of refence electrodes based on the distribution of a strongly ...
Determination of Selected Natural Psychoactive Substances in Organic Matrices at 3D Printed Electrodes
Choińska-Mlynarczyk, Marta; Šestáková, Ivana; Navrátil, Tomáš
2023 - English
Psilocybin and its derivative psilocin are popular psychoactive substances both as experimental\ntreatments in clinical trials and as illicit drugs. Their potential ability to influence the human\nbrain entails the need for a fast, inexpensive, selective, and sensitive method of their\ndetermination. The aim of our study was the development of new 3D-printed electrodes which\nfulfill these demands and are useful for medical, toxicological, and forensic purposes.\nSuccessful development allows determining in real matrices (human plasma and dried\nmushrooms) concentrations of the order of 1 μmol dm-3.\n
Keywords:
natural psychoactive substances; 3D-printed electrodes; psilocin; psilocybin
Available on request at various institutes of the ASCR
Determination of Selected Natural Psychoactive Substances in Organic Matrices at 3D Printed Electrodes
Psilocybin and its derivative psilocin are popular psychoactive substances both as experimental\ntreatments in clinical trials and as illicit drugs. Their potential ability to influence the ...
On the structure and values of betweenness centrality in dense betweenness-uniform graphs
Ghanbari, B.; Hartman, David; Jelínek, V.; Pokorná, Aneta; Šámal, R.; Valtr, P.
2023 - English
Betweenness centrality is a network centrality measure based on the amount of shortest paths passing through a given vertex. A graph is betweenness-uniform (BUG)if all vertices have an equal value of betweenness centrality. In this contribution, we focus on betweenness-uniform graphs with betweenness centrality below one. We disprove a conjecture about the existence of a BUG with betweenness value α for any rational numberαfrom the interval (3/4,∞) by showing that only very few betweenness centrality values below 6/7 are attained for at least one BUG. Furthermore, among graphs with diameter at least three, there are no betweenness-uniform graphs with a betweenness centrality smaller than one. In graphs of smaller diameter, the same can be shown under a uniformity condition on the components of the complement.
Keywords:
betweenness; graphs
Available in digital repository of the ASCR
On the structure and values of betweenness centrality in dense betweenness-uniform graphs
Betweenness centrality is a network centrality measure based on the amount of shortest paths passing through a given vertex. A graph is betweenness-uniform (BUG)if all vertices have an equal value of ...
Adaptation of methods for cyclo-stationary processes for noisy structural health data
Fischer, Cyril; Bayer, Jan; Náprstek, Jiří; Urushadze, Shota
2023 - English
In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. Conversely, the desired attributes under scrutiny are periodic in nature. Thus, methodologies designed to identify cyclo-stationary properties within noisy data can be adapted for such scenarios, assuming an adequate length of the recorded data.
Keywords:
data analysis; cyclo-stationary processes; structural health monitoring
Available at various institutes of the ASCR
Adaptation of methods for cyclo-stationary processes for noisy structural health data
In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. ...
Consistency of mathematical and experimental model of the autoparametric system
Fischer, Cyril; Náprstek, Jiří
2023 - English
This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy sphere in a spherical surface. It shows that the danger posed by the potentially unstable self-parametric nature of the mathematical system is not too great in the case of realistic configurations, and that the values of the parameters describing the realistic structures remain within intervals corresponding to the stable behaviour of the absorber.
Keywords:
vibration absorber; rolling sphere; spherical surface; autoparametric system; structural health monitoring
Available at various institutes of the ASCR
Consistency of mathematical and experimental model of the autoparametric system
This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy ...
Ceramic protection of anti-corrosion layers of 3-glycidyloxypropyl-triethoxysilane on steel
Pokorný, P.; Prodanović, N.; Janata, Marek; Brožek, Vlastimil
2023 - English
There are various variations on the problem of steel reinforcement bond strength in concrete. Along with geometrical considerations, corrosion performance of steels with varying chemical compositions in interaction with variable chemical compositions of concrete are crucial. One approach is to cover steel surfaces with organosilane compounds, which increases the reinforcement resistance to corrosion in both acidic and alkaline conditions but, on the other hand, may weaken the reinforcement bond strength on concrete. The issue is resolved by intentionally forming a thin-walled, highly adhering corundum layer that is highly porous and impregnated with 3-glycidyloxypropyltriethoxysilane. This procedure also includes testing the adhesion properties between the ceramic and the metal and the cement prior to conducting a corrosion test in a chloride environment.
Keywords:
steel; concrete; ceramics
Available at various institutes of the ASCR
Ceramic protection of anti-corrosion layers of 3-glycidyloxypropyl-triethoxysilane on steel
There are various variations on the problem of steel reinforcement bond strength in concrete. Along with geometrical considerations, corrosion performance of steels with varying chemical compositions ...
On the development of a numerical model for the simulation of air flow in the human airways
Lancmanová, Anna; Bodnár, Tomáš; Sequeira, A.
2023 - English
This contribution reports on an ongoing study focusing on reduced order models for incompressible viscous fluid flow in two dimensional channels. A finite difference solver was developed using a simple implementation of the immersed boundary method to represent the channel geometry. The solver was validated for unsteady flow by comparing the obtained two-dimensional numerical solutions with analytical profiles computed from the Womersley solution. Finally the 2D model was coupled to a simple 1D extension simulating the flow in axisymmetric elastic vessel (tube). Some of the coupling principles and implementation issues are discussed in detail.
Keywords:
reduced order model; incompressible Navier-Stokes equations; finite difference approximation; coupling method
Available in digital repository of the ASCR
On the development of a numerical model for the simulation of air flow in the human airways
This contribution reports on an ongoing study focusing on reduced order models for incompressible viscous fluid flow in two dimensional channels. A finite difference solver was developed using a ...
Simulating particle-laden flows: from immersed boundaries towards model order reduction
Isoz, Martin; Kubíčková, Lucie; Kotouč Šourek, M.; Studeník, Ondřej; Kovárnová, A.
2023 - English
Particle-laden flow is prevalent both in nature and in industry. Its appearance ranges from the trans-port of riverbed sediments towards the magma flow, from the deposition of catalytic material inside particulate matter filters in automotive exhaust gas aftertreatment towards the slurry transport in dredging operations. In this contribution, we focus on the particle-resolved direct numerical simulation (PR-DNS) of the particle-laden flow. Such a simulation combines the standard Eulerian approach to computational fluid dynamics (CFD) with inclusion of particles via a variant of the immersed boundary method (IBM) and tracking of the particles movement using a discrete element method (DEM). Provided the used DEM allows for collisions of arbitrarily shaped particles, PR-DNS is based (almost) entirely on first principles, and as such it is a truly high-fidelity model. The downside of PR-DNS is its immense computational cost. In this work, we focus on three possibilities of alleviating the computational cost of PR-DNS: (i) replacing PR-DNS by PR-LES or PR-RANS, while the latter requires combining IBM with wall functions, (ii) improving efficiency of DEM contact solution via adaptively refined virtual mesh, and (iii) developing a method of model order reduction specifically tailored to PR-DNS of particle-laden flows.
Keywords:
particle-laden flow; CFD-DEM; arbitrarily-shaped particles; finite volume method
Fulltext is available at external website.
Simulating particle-laden flows: from immersed boundaries towards model order reduction
Particle-laden flow is prevalent both in nature and in industry. Its appearance ranges from the trans-port of riverbed sediments towards the magma flow, from the deposition of catalytic material ...
On Reynolds-averaged turbulence modeling with immersed boundary method
Kubíčková, Lucie; Isoz, Martin
2023 - English
The immersed boundary (IB) method is an approach in the computational fluid dynamics in which complex geometry conforming meshes are replaced by simple ones and the true simulated geometry is projected onto the simple mesh by a scalar field and adjustment of governing equations. Such an approach is particularly advantageous in topology optimizations (TO) where it allows for substantial speed-up since a single mesh can be used for all the tested topologies. In our previous work, we linked our custom IB variant, the hybrid fictitious domain-immersed boundary method (HFDIB), with a TO framework and successfully carried out an optimization under laminar flow conditions. However, to allow for optimizations of reallife components, the IB approach needs to be coupled with an affordable turbulence modeling. In this contribution, we focus on extending the HFDIB approach by the possibility to perform Reynolds-averaged simulations (RAS). In particular, we implemented the k − ω turbulence model and wall functions for closure variables and velocity.
Keywords:
immersed boundary; RAS; wall functions; CFD; OpenFOAM
Fulltext is available at external website.
On Reynolds-averaged turbulence modeling with immersed boundary method
The immersed boundary (IB) method is an approach in the computational fluid dynamics in which complex geometry conforming meshes are replaced by simple ones and the true simulated geometry is ...
Finite element modal analysis of a silicone vocal fold filled with fluid
Hájek, P.; Radolf, Vojtěch; Horáček, Jaromír; Švec, J. G.
2023 - English
A three dimensional (3D) finite element (FE) model of a silicone vocal fold (VF) filled with fluid is presented here. The silicone part of the model is based on partial differential equations of the continuum mechanics and consider large deformations. The fluid domain encapsulated in the silicone VF is defined semianalytically as a lumped-element model describing the fluid in hydrostatic conditions. The elongated and pressurized silicone VF was subjected to perturbed modal analysis. Results showed that the choice of the fluid inside the VF substantially influences the natural frequencies. Namely, the water-filling lowers the natural frequencies approximately by half over the air-filling. Besides, the procedure of reverse engineering for obtaining the geometry of the VF from already 3D-printed mold is introduced.
Keywords:
perturbed modal analysis; finite element method; vocal folds; reverse engineering; biomechanics of voice
Fulltext is available at external website.
Finite element modal analysis of a silicone vocal fold filled with fluid
A three dimensional (3D) finite element (FE) model of a silicone vocal fold (VF) filled with fluid is presented here. The silicone part of the model is based on partial differential equations of the ...
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