Mathematical model for determining the viscoelastic properties of soft tissues using indentation tests

grants projects TG01010117 – PROSYKO and SGS Technical University of Liberec

Fluid structure interaction in fully collapsible tubes

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.The main goal of the developed theory is to formulate the biomechanical conditions (geometrical dimensions, viscoelastic properties of veins and blood fluid flow conditions) at which an unstable behavior or even the vein collapse can occur. The above problems are numerically modeled by the finite element method. The weak formulation of the tube deformation is based on the virtual work principle. The mixed formulation of the finite element method with the separately interpolated pressure is used for the structure. The strong coupling of both structure and fluid solvers allow us to simulate self-induced large deflection oscillations of the tube. Provided that the Neo-Hook’s material model was applied the analytical formula for the collapse conditions was found. It was proved that for the brain vein contraction about 5%, the vein collapse can occurs even under normal physiological condition – the angiosynizesis. The fluid structure interaction is studied experimentally on the special experimental line. The fluid structure phenomenon is investigated both for the continuous and pulsating flow and it is evaluated by a non-invasive optical. The method is based on optical measurements of radial displacement of the pulsating tube wall. The simultaneous clinics observation (histological findings), in vitro experiments and numerical modeling gives sufficient data to predict biomechanical conditions of the angiosynizesis.mp201

Infrared study of the spin reorientation transition and its reversal in the superconducting state in underdoped Ba1−xKxFe2As2{\mathrm{Ba}}_{1-x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}

With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba1−xKxFe2As2. In agreement with the predicted transition from a single-Q to a double-Q AF structure, we found that a distinct spin density wave develops in the t-AF phase. The pair breaking peak of this spin density wave acquires much more low-energy spectral weight than the one in the o-AF state which indicates that it competes more strongly with superconductivity. We also observed additional phonon modes in the t-AF phase which likely arise from a Brillouin-zone folding that is induced by the double-Q magnetic structure with two Fe sublattices exhibiting different magnitudes of the magnetic moment

Infrared ellipsometry study of photogenerated charge carriers at the (001) and (110) surfaces of SrTiO3\mathrm{SrTi}{\mathrm{O}}_{3} crystals and at the interface of the corresponding LaAlO3/SrTiO3\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3} heterostructures

With infrared (IR) ellipsometry and dc resistance measurements, we investigated the photodoping at the (001) and (110) surfaces of SrTiO3 (STO) single crystals and at the corresponding interfaces of LaAlO3/SrTiO3 (LAO/STO) heterostructures. In the bare STO crystals, we find that the photogenerated charge carriers, which accumulate near the (001) surface, have a similar depth profile and sheet carrier concentration as the confined electrons that were previously observed in LAO/STO (001) heterostructures. A large fraction of these photogenerated charge carriers persist at low temperature at the STO (001) surface even after the ultraviolet light has been switched off again. These persistent charge carriers seem to originate from oxygen vacancies that are trapped at the structural domain boundaries, which develop below the so-called antiferrodistortive transition at T∗=105K. This is most evident from a corresponding photodoping study of the dc transport in STO (110) crystals for which the concentration of these domain boundaries can be modified by applying a weak uniaxial stress. The oxygen vacancies and their trapping by defects are also the source of the electrons that are confined to the interface of LAO/STO (110) heterostructures, which likely do not have a polar discontinuity as in LAO/STO (001). In the former, the trapping and clustering of the oxygen vacancies also has a strong influence on the anisotropy of the charge carrier mobility. We show that this anisotropy can be readily varied and even inverted by various means, such as a gentle thermal treatment, UV irradiation, or even a weak uniaxial stress. Our experiments suggest that extended defects, which develop over long time periods (of weeks to months), can strongly influence the response of the confined charge carriers at the LAO/STO (110) interface

Temperature-driven topological phase transition and intermediate Dirac semimetal phase in ZrTe5{\mathrm{ZrTe}}_{5}

We present an infrared spectroscopy study of ZrTe5, which confirms a recent theoretical proposal that this material exhibits a temperature-driven topological quantum phase transition from a weak to a strong topological insulating state with an intermediate Dirac semimetal state around Tp ≃ 138 K. Our study details the temperature evolution of the energy gap in the bulk electronic structure. We found that the energy gap closes around Tp, where the optical response exhibits characteristic signatures of a Dirac semimetal state, i.e., a linear frequency-dependent optical conductivity extrapolating to the origin (after subtracting a weak Drude response). This finding allows us to reconcile previous diverging reports about the topological nature of ZrTe5 in terms of a variation of Tp that depends on the crystal growth condition

Optimized calibration and measurement procedures in rotating analyzer and rotating polarizer ellipsometry

Accurate spectroellipsometric (SE) measurements in the rotating analyzer (RAE) or rotating polarizer (RPE) configurations require accurate values of the polarizer/analyzer(/retarder) azimuths. While the readings are usually fairly accurate, true values are influenced by possible offsets between the plane of incidence, physical axes of the elements, and the instrument scales. The offsets are often determined by specialized calibration procedures. We describe SE measurements designed to obtain the calibration parameters together with the target ellipsometric spectra. We use multiple settings of the polarizer (analyzer) azimuths in RAE (RPE), respectively, to optimize precision and accuracy of SE measurements, and to economize measurement time. The optimization concerns the choice of measurement parameters as well as the subsequent data analysis. We present in detail examples of visible-ultraviolet measurements

Modelling of the TCPC geometry effects on hemodynamics of the cardiovascular system with one functionally ventricle

This action is realized by the project NEXLIZ - CZ.1.07/2.3.00/30.0038, which is co-financed by the European social fund and the state budget of the Czech republic

Mathematical model for determining the viscoelastic properties of soft tissues using indentation tests

grants projects TG01010117 – PROSYKO and SGS Technical University of Liberec