Papers by Frantisek Marsik
The authors study the movement of the brain intracranially and the study hemodynamic problems in ... more The authors study the movement of the brain intracranially and the study hemodynamic problems in the brain a long time. In this presentation they study the material's duality of bridging brain veins, the first not only microscopically description, but the quantification of vein's wall, especially first of all. The authors study the movement of brain intracranially on 256 patients. From study, study of exchanges correlation ICP/CPP in time, together with the new study of quantity and qualities of bridging vein's wall, the authors are begin to open the hypothesis and new studies of function this bridging veins. The authors show the any functional correlations between the bridging veins and function of the cavernous sinus as pulsing pump in the end of the presentation.
Continuum mechanics and thermodynamics, May 10, 2024
The current paper presents a theoretical analysis of swirl flow stability, both inside a tube (vo... more The current paper presents a theoretical analysis of swirl flow stability, both inside a tube (vortex tube) and in a free annular swirl flow. The starting concept is the study of the evolution of velocity and temperature fluctuations. Methods of non-equilibrium thermodynamics are used to describe the magnitude of fluctuations and their properties. The important role of the total enthalpy follows from a variational analysis. Moreover, the thermodynamic criterion of the stability is formulated using the total enthalpy, and compared with experiments, numerical results and classical Rayleigh theory support its applicability. It was shown that the solid body vortex is at the margin of stability, which is experimentally observed. Analogously, the potential vortex is by the thermodynamic criterion stable; however, by the Rayleigh criteria it is on the onset of stability. The classical Taylor experiment of flow between two rotating cylinders is analysed from the point of view of this criterion. These results are underlined by swirl tube experiments at the Institute of Aerospace Thermodynamics at Stuttgart University and the annular nozzle experiments performed in the Institute of Thermomechanics CAS in Prague. Both independent experiments confirm the transformation of the initial annular vortex into a stable potential-type vortex. The results of this theory can also be used to explain the exceptional stability of tropical cyclones.
Acta of Bioengineering and Biomechanics, 2001
Archives of Thermodynamics, 2003
The Sedláček's turbine (known as SETUR) is an interesting hydraulic device that converts hydrauli... more The Sedláček's turbine (known as SETUR) is an interesting hydraulic device that converts hydraulic energy into mechanical motion. The rotor in this turbine is blade-less and has a completely smooth shape. To find a physical explanation of its operation is an open problem, which we tackle here. Our theory is based on the idea that the fluid force on the rotor exists as a positive feedback to the orbital motion of the rotor. This is explained in a theoretical computation and supported by a numerical experiment.
Cardiovascular Engineering, Dec 1, 2004
The uptake of the drugs by human organisms has long been one of the primary concerns of pharmacol... more The uptake of the drugs by human organisms has long been one of the primary concerns of pharmacological research. The numerical model of the human cardiovascular and respiratory system with the baroreflex and chemoreflex regulation including the physiologically-based pharmacokinetic model and also the model of the drug-cardiac cell channels interaction is developed at the IT CAS. The 24th segments model of pulsating type imitating the electrochemical and mechanical activity of heart muscle was used to the simulation of the antiarrhythmic drug (propranolol) effects on the themodynamic and physiologically behaviour of these systems.
PubMed, Sep 1, 2010
Understanding of the bone remodelling process has considerably increased during the last 20 years... more Understanding of the bone remodelling process has considerably increased during the last 20 years. Since the ability to simulate (and predict) the effects of bone remodelling offers substantial insights, several models have been proposed to describe this phenomenon. The strength of the presented model is that it includes biochemical control factors (e.g., the necessity of cell-to-cell contact, which is mediated by the RANKL-RANK-OPG chain during osteoclastogenesis) and mechanical stimulation, the governing equations are derived from interaction kinetics (e.g., mass is preserved in running reactions), and the parameters are measurable. Behaviour of the model is in accordance with experimental and clinical observations, such as the role of dynamic loading, the inhibitory effect of dynamic loading on osteoclastogenesis, the observation that polykaryon osteoclasts are activated and formed by a direct cell-to-cell contact, and the correct concentrations of osteoblasts, osteoclasts, and osteocytes. The model does not yet describe the bone remodelling process in complete detail, but the implemented simplifications describe the key features and further details of control mechanisms may be added.
Advances in Engineering Software, Nov 1, 2007
International Journal of Hydrogen Energy, Jun 1, 2013
ABSTRACT It is common knowledge that efficiency of fuel cells is highest when no electric current... more ABSTRACT It is common knowledge that efficiency of fuel cells is highest when no electric current is produced while when the fuel cell is really working, the efficiency is reduced by dissipation. In this paper the relation between efficiency and dissipation inside the fuel cell is formulated within the framework of classical irreversible thermodynamics of mixtures. It is shown that not only dissipation influences the efficiency but that there are also some other terms which become important if there are steep temperature gradients inside the fuel cell. Indeed, we show that the new terms are negligible in polymer-electrolyte membrane fuel cells while they become important in solid oxide fuel cells. In summary, this paper presents a formulation of non-equilibrium thermodynamics of fuel cells and provides analysis of efficiency in terms of processes inside the fuel cells, revealing some new terms affecting the efficiency.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika, 2003
Mathematics and Computers in Simulation, Feb 1, 2010
Remodelling is a dynamic process occurring during growth and it includes sensing of environmental... more Remodelling is a dynamic process occurring during growth and it includes sensing of environmental changes, tissue resorbance, i.e. the removal of existing old bone, and formation of new tissue. The biomechanical remodelling process is relatively well formulated for bones and can be divided into three stages: (1) bone resorption based on the osteoclast activity, (2) bone deposition based on the osteoblast activity and (3) bone growth control established on RANK/RANKL/OPG pathway-RANKL/OPG balance. The main driving force of remodelling process is a dynamic loading (cyclic compression and expansion, e.g. walking or running), which strongly influences the rate of chemical reactions. The evolution from the homogeneous density distribution to the corticalis and cancellous bone formation is shown. An inevitable influence of a dynamic mechanical loading and osteoprotegerin (OPG) concentration is demonstrated. Deformations were calculated by commercial code ANSYS. The clinical experience indicates that the dynamic loading (above the threshold level 1500-2500 microstains/s), especially walking with a characteristic time approximately 1 s, influences the whole process of bone remodelling after a time period of approximately 3 months. The numerical simulation shows that the concentration of the new bone and the bone elastic constants substantially depend on history and intensity of the loading, drug delivery and nutrition.
Journal of Non-Equilibrium Thermodynamics, 1994
A general equation for muscle energy balance is derived, describing irreversible macroscopic proc... more A general equation for muscle energy balance is derived, describing irreversible macroscopic processes of energy transformation in a muscle as a whole, and the interaction of the muscle with its surroundings. The formulation of the equation stems from the balances of mass, mechanical energy, internal energy and entropy. The equation involves isotonic and isometric contractions, as well as energy dissipation stimulated in a non-contracting state. For an isotonic muscle contraction our formulation approximates the Hill equation. An isometric contraction is approximated by the time-dependence of the external muscle force, involving the fluxes of heat and mass. Using the implicit dissipative component of a pressure tensor (sometimes called the "friction clutch" mechanism), the external force can be expressed in units of power, and this can be quantitatively compared with two other muscle loading states. A noncontracting, energy-dissipative muscle is characterized by an uncoupling between the power of chemical reactions and the dissipative part of the tension tensor; the dissipated energy then manifests itself in fluxes of heat and mass. The quantitative estimation of the dissipative power of a muscle under various physiological conditions should clarify the general role of a muscle, including its dissipative non-contracting state. Introduction The skeletal muscle is considered to be at once a chemo-mechanical converter whose primary function in the organism is the generation of force, and the converter that provides, during increased metabolic rate in a non-contracting state, chemical work, mass and energy fluxes. Caplan [1] applied the concepts of irreversible thermodynamics to the chemo-mechanical coupling underlying an isotonic contraction and derived Hill's force-velocity relation. His model is in agreement with biochemical data J. Non-Equilib. Thermodyn. Vol. 19,1994, No. 3 © Copyright 1994 Walter de Gruyter · Berlin · New York 198 F. Marsik, J. Mejsnar [2]. The same formalism of irreversible thermodynamics, applied to the chemomechanical coupling underlying an isometric contraction [3], allows a new analysis of the fundamental process of energy transduction in an idealized unit element of contractile material, even without the evaluation of the mechanical external response. There is one model of smooth muscle contraction [4], capable of describing the active force under various conditions of contraction, including isometric twitch; similar to the model presented here, it is based on the transformation of chemical energy into mechanical energy via the cross-bridge extending from the myosin to the action filaments, the so-called "friction clutch" mechanism. This model, however, can not be used for the evaluation of the increased metabolic rate of a non-contracting muscle. A general equation is introduced for the entropy production (Section 4), describing irreversible macroscopic processes of energy transformation in a muscle under conditions of both types of contraction, and in a non-contracting dissipative state, as well as interactions of the muscle with its surroundings. The general equation of the muscle energy balance is derived from the balance laws in Section 2. 2. Balance laws A systematic macroscopic description of non-equilibrium processes in a muscle must be built upon the first and second law of thermodynamics, i.e. upon the law of conservation of energy and the law of entropy. It is, however, necessary to formulate these laws in a way suitable for the purposes of muscular energetics. This implies that the variables acting in these laws are given by i) the balance laws for a continuous muscle system, balance (conservation) of mass, momentum and mechanical energy; and ii) the constitutive laws following from irreversible thermodynamics. consider that the system has 2.1 Conservation of mass The rate of change of a chemical component á in volume y (of the muscle) is:
Journal of Physical Chemistry B, Oct 15, 2009
This paper offers a theoretical explanation of the coupling effect phenomenon between mechanical ... more This paper offers a theoretical explanation of the coupling effect phenomenon between mechanical loading and chemical reactions based on linear nonequilibrium thermodynamics and also discusses the classical method of obtaining restrictions on the phenomenological coefficients. The question whether static or dynamic loading influences biochemical processes is addressedsthe necessity of dynamic loading as a stimulatory mechanism is shown. Further, the presented paper suggests that chemical and mechanical processes do not only facilitate or support one another but they may also play a triggering role for the other coupled processssome biochemical processes may need mechanical stimulation to run and vice versa as wellschemical reactions may provide energy for some mechanical processes. As an example, a detailed analysis of a model for controlled autocatalytic reproduction is presented, where the coupling effect, i.e. the influence of dynamic loading on reaction kinetics, is demonstrated.
Continuum Mechanics and Thermodynamics, Feb 8, 2023
In this article, acknowledgement section should have read 'This paper was conducted as part of th... more In this article, acknowledgement section should have read 'This paper was conducted as part of the student grant competition SP2022/28: Research in the field of raw materials crushing and determination of thermodynamic properties as a function of grain size for the design of process and treatment plants. The paper has been also done in connection with project Innovative and additive manufacturing technology-new technological solutions for 3D printing of metals and composite materials, reg. no. CZ.02.1.
Materials Science and Engineering, May 1, 1987
Abstract A draft of a new method for the simulation of the coarsening of carbides under spatially... more Abstract A draft of a new method for the simulation of the coarsening of carbides under spatially non-homogeneous conditions was elaborated. For calculations the time and the local variations in the concentration of the carbide-forming elements, the temperature, the mechanical stress etc. can be considered. The method can be used to solve approximately examples with complex carbides. This method is suitable for application to a solution induced by the diffusion transfer of elements over the surface of a body.
Journal of Non-Equilibrium Thermodynamics, 1989
The generalized thermodynamic stability criterion is used to derive the stability limits of trans... more The generalized thermodynamic stability criterion is used to derive the stability limits of transonic fluid flow. The important role of dissipation for the stability of hyperbolic problems is shown physically, numerically and experimentally. In the numerical procedure, dissipation is described by a so-called numerical viscosity μ η , which is proportional to the ratio of the modified physical viscosity μ to the thickness Ax s " of the corresponding shock wave, i.e., μ η^1-Μ" 2 β μ*
Cardiovascular Engineering, Dec 1, 2007
This research is aimed to the determination of the changes in the cardiac energetic output for th... more This research is aimed to the determination of the changes in the cardiac energetic output for three different modes of cardiac rhythm pacing. The clinical investigation of thirteen patients with the permanent dualchamber pacemaker implantation was carried out. The patients were taken to echocardiography examination conducted by way of three pacing modes (AAI, VVI and DDD). The myocardial energetic parameters-the stroke work index (SWI) and the myocardial oxygen consumption (MVO2) are not directly measurable, however, their values can be determined using the numerical model of the human cardiovascular system. The 24-segment hemodynamical model (pulsating type) of the human cardiovascular system was used for the numerical simulation of the changes of myocardial workload for cardiac rhythm pacing. The model was fitted by well-measurable parameters for each patient. The calculated parameters were compared using the two-tailed Student's test. The differences of SWI and MVO2 between the modes AAI and VVI and the modes DDD and VVI are statistically significant (P \ 0.05). On the other hand, the hemodynamic effects for the stimulation modes DDD and AAI are almost identical, i.e. the differences are statistically insignificant (P [ 0.05).
Continuum Mechanics and Thermodynamics, Jan 12, 2023
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Papers by Frantisek Marsik