Number of found documents: 863
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Deformation behaviour of gellan gum based artificial bone structures under simulated physiological conditions
Krčmářová, N.; Šleichrt, J.; Fíla, Tomáš; Koudelka_ml., Petr; Kytýř, Daniel
2017 - English
The paper deals with investigation of deformation behaviour of gellan gum (GG) based\nstructures prepared for regenerative medicine purposes. Investigated material was synthesized as porous spongy-like scaffold reinforced by bioactive glass (BAG) nano-particles in different concentrations. Deformation behavior was obtained employing custom designed experimental setup. This device equipped with bioreactor chamber allows to test the delivered samples under simulated physiological conditions with controlled flow and temperature. Cylindrical samples were subjected to uniaxial quasi-static loading in tension and compression. Material properties of plain scaffold buffered by 50 wt% and 70 wt% BAG were derived from a set of tensile and compression tests. The results are represented in form of stress-strain curves calculated from the acquired force and displacement data. Keywords: gellan gum scaffold; reinforcement; uni-axial loading; simulated physiological conditions Available at various institutes of the ASCR
Deformation behaviour of gellan gum based artificial bone structures under simulated physiological conditions

The paper deals with investigation of deformation behaviour of gellan gum (GG) based\nstructures prepared for regenerative medicine purposes. Investigated material was synthesized as porous ...

Krčmářová, N.; Šleichrt, J.; Fíla, Tomáš; Koudelka_ml., Petr; Kytýř, Daniel
Ústav teoretické a aplikované mechaniky, 2017

Non-holonomic planar and spatial model of a ball-type tuned mass damping device
Náprstek, Jiří; Fischer, Cyril
2017 - English
The area of tuned mass dampers is a wide field of inspiration for theoretical studies in non-linear dynamics and dynamic stability. The studies attempt to estimate behaviour of diverse damping devices and their reliability. The current paper deals with the response of a heavy ball rolling inside a spherical cavity under horizontal kinematic excitation. The non-linear system consists of six degrees of freedom with three non-holonomic constraints. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appell-Gibbs function of acceleration energy is developed and discussed. Comparison with previous planar (SDOF) model which is based on the Lagrangian procedure is given. The system has an auto-parametric character and therefore semi-trivial solutions and their dynamic stability can be analysed. The most important post-critical regimes are outlined and qualitatively evaluated in resonance domain. Numerical experiments were performed when excitation frequency is slowly swept up and down to identify different modes of response. Some applications in civil engineering as a tuned mass damper, which can be used on slender structures, are mentioned. The proposed device is compared with a conventional pendulum damper. Strengths and weaknesses of both absorbers types\nare discussed. Keywords: tuned mass damper; moving ball; Appell-Gibbs formulation Available at various institutes of the ASCR
Non-holonomic planar and spatial model of a ball-type tuned mass damping device

The area of tuned mass dampers is a wide field of inspiration for theoretical studies in non-linear dynamics and dynamic stability. The studies attempt to estimate behaviour of diverse damping devices ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2017

Remarks on inverse of matrix polynomials
Fischer, Cyril; Náprstek, Jiří
2017 - English
Analysis of a non-classically damped engineering structure, which is subjected to an external excitation, leads to the solution of a system of second order ordinary differential equations. Although there exists a large variety of powerful numerical methods to accomplish this task, in some cases it is convenient to formulate the explicit inversion of the respective quadratic\nfundamental system. The presented contribution uses and extends concepts in matrix polynomial theory and proposes an implementation of the inversion problem. Keywords: matrix polynomial; polynomial eigenvalues; structural vibration Available at various institutes of the ASCR
Remarks on inverse of matrix polynomials

Analysis of a non-classically damped engineering structure, which is subjected to an external excitation, leads to the solution of a system of second order ordinary differential equations. Although ...

Fischer, Cyril; Náprstek, Jiří
Ústav teoretické a aplikované mechaniky, 2017

Formace polymorfů uhličitanu vápenatého během mísení koncentrovaných roztoků solí
Ševčík, Radek; Mácová, Petra; Viani, Alberto
2017 - Czech
Příspěvek se zaobírá předběžnými výsledky studia gelové fáze vznikající během mísení koncentrovaných roztoků solí během syntézy polymorfů uhličitanu vápenatého.\nBěhem reakce bylo odebráno několik vzorků, které byly následně zkoumány instrumentálními technikami jako např. skenovací elektronový mikroskop. This contribution is demonstrated the preliminary results of the study of the gel phase forming during the synthesis of calcium carbonate's polymorphs.\nSeveral samples were collected during the reaction and they were subsequently investigated with instrumental techniques e.g. scanning electron microscopy. Keywords: CaCO3; polymorphs; synthesis; vaterite; ACC Available at various institutes of the ASCR
Formace polymorfů uhličitanu vápenatého během mísení koncentrovaných roztoků solí

Příspěvek se zaobírá předběžnými výsledky studia gelové fáze vznikající během mísení koncentrovaných roztoků solí během syntézy polymorfů uhličitanu vápenatého.\nBěhem reakce bylo odebráno několik ...

Ševčík, Radek; Mácová, Petra; Viani, Alberto
Ústav teoretické a aplikované mechaniky, 2017

Stochastic stability of the generalized van der Pol system under random additive excitation
Náprstek, Jiří; Fischer, Cyril
2017 - English
The paper is motivated by a series of wind tunnel experiments investigating aeroelastic SDOF and TDOF section models of various shape and aeroelastic properties. It reveals that most of them can be theoretically modeled by the van der Pol – Duffing type equations or their combination adjusting degree of individual nonlinear terms or their coefficients. It should be emphasized that this character of the system response is very stable and is obvious in linear as well as in weakly nonlinear domain when the post-critical effect emerges. Moreover, many special effects identified by an experimental way evoke properties recognized in the pure theory of differential equations. Keywords: wind tunnel experiment; random excitation; stochastic stability Available at various institutes of the ASCR
Stochastic stability of the generalized van der Pol system under random additive excitation

The paper is motivated by a series of wind tunnel experiments investigating aeroelastic SDOF and TDOF section models of various shape and aeroelastic properties. It reveals that most of them can be ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2017

Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level
Krčmářová, Nela; Šleichrt, J.; Doktor, T.; Kytýř, Daniel; Jiroušek, O.
2017 - English
Metal foams are innovative porous material used for wide range of application such as\ndeformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose.\nIn this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465 HV1.019 and average Vickers hardness of ALCORAS was 36.585 HV1.019. Keywords: metal foam; Vickers hardness; cell-wall; indentation under low loads Available at various institutes of the ASCR
Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level

Metal foams are innovative porous material used for wide range of application such as\ndeformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict ...

Krčmářová, Nela; Šleichrt, J.; Doktor, T.; Kytýř, Daniel; Jiroušek, O.
Ústav teoretické a aplikované mechaniky, 2017

Microscopic features of cement paste modified by fine perlite
Hrbek, V.; Koudelková, Veronika; Padevět, P.; Šašek, Petr
2017 - English
The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight aggregate enhancing the insulating performance of concrete. This paper focuses on\nintegration of fine perlite into the cement matrix and possible replacement of the cement binder in\nthe composition of the material. The macromechanical performance of the modified paste is tested on specimens with 5, 10, 15 and 20% fine perlite substitution and pure cement sample. To distinguish the effect of the perlite on the microstructural level, pure cement material and specimen containing 10% of fine perlite are investigated by the electron microscopy. Furthermore, the mechanical properties of individual phases are examined and compared on same samples by instrumented indentation. The presented results enabled estimation of fine perlite impact on the macro and microscopic performance of the material. Keywords: perlite; SEM; nanoindentation; mechanical properties Available at various institutes of the ASCR
Microscopic features of cement paste modified by fine perlite

The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight ...

Hrbek, V.; Koudelková, Veronika; Padevět, P.; Šašek, Petr
Ústav teoretické a aplikované mechaniky, 2017

A concept for testing and monitoring of building structures – theoretical case study
Bayer, Jan
2017 - English
A mere comparison of measured and analytical deformations, natural frequencies and mode\nshapes provides us with just a small part of the information contained in the data, especially when component- level damage prevention is needed. The presented analysis studies in detail a few criteria for evaluation of measured data, with the example of simulated plane trusses in respect to the ultimate limit state. It demonstrates the high potential of a systematic approach, while combining several criteria, particularly when using simultaneous strain and deformation measurements, as it documents the proposed Relative Mode Difference (RMD) criterion. On the other hand, the study points out the major limitation of practical applications that is caused by unknown inherent uncertainties of various kinds, providing us with the incentive for further experimental research. Keywords: testing; monitoring; building structures; ultimate limit state; mode shapes; strains Available at various institutes of the ASCR
A concept for testing and monitoring of building structures – theoretical case study

A mere comparison of measured and analytical deformations, natural frequencies and mode\nshapes provides us with just a small part of the information contained in the data, especially when component- ...

Bayer, Jan
Ústav teoretické a aplikované mechaniky, 2017

Lyapunov exponents – practical computation
Fischer, Cyril; Náprstek, Jiří
2017 - English
The Lyapunov exponents serve as numerical characteristics of dynamical systems, which measure possible divergence of nearby trajectories of the solution. In this way they express dependence of the dynamical system on initial conditions. However, the value of Lyapunov exponents consists in their ability to characterise deterministic chaos. The limiting process intrinsic in the definition of Lyapunov exponents, unfortunately, seriously complicates their computation. The short paper presents an overview of difficulties in numerical approaches to enumeration of Lyapunov exponents or at least the largest one and shows a promising method based on QR decomposition of the system Jacobian. Keywords: Lyapunov exponent; dynamical system; non-linear system Available at various institutes of the ASCR
Lyapunov exponents – practical computation

The Lyapunov exponents serve as numerical characteristics of dynamical systems, which measure possible divergence of nearby trajectories of the solution. In this way they express dependence of the ...

Fischer, Cyril; Náprstek, Jiří
Ústav teoretické a aplikované mechaniky, 2017

Triangulated medieval cities
Loits, André; Drdácký, Tomáš; Buzek, Jaroslav; Zadražil, Tomáš
2017 - English
The paper presents a long term research work addressing sometimes not so evident values of historic cities; which are linked with geometric (urban) relations between the architectural elements set in cities. the position of city boundary (walls), market place and street layout was an intentional concept, not a result of unorganized building activities of new colonists. It is known from the archive and historic data, and verified by archaeological findings that the founded cities were planned. It is evident that cities seemingly different are organized following certain rules and methods. The work supports the hypothesis that original concept of the city survived in its pattern and structure until today and is one of the values expressing its individual and original identity. Hypothetic Medieval triangulation method, developed by André Loits is presented on case studies of České Budějovice, Kadaň and Klatovy. The method was so far used for the analysis of 30 selected Town Heritage Reserves and Zones and identifies two basi "schools" in location concepts of studied cities. Keywords: historic cities; location; medieval triangulation; urban pattern; urban heritage values Available at various institutes of the ASCR
Triangulated medieval cities

The paper presents a long term research work addressing sometimes not so evident values of historic cities; which are linked with geometric (urban) relations between the architectural elements set in ...

Loits, André; Drdácký, Tomáš; Buzek, Jaroslav; Zadražil, Tomáš
Ústav teoretické a aplikované mechaniky, 2017

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