10 results on '"*ANISOTROPY"'
Search Results
2. Fixel-based analýza mozku u pacientů po první epizodě schizofrenie.
- Author
-
Slezák, Ondřej, Škoch, Antonín, Žižka, Jan, Bayer, David, Španiel, Filip, Tintěra, Jaroslav, Vaňásek, Jiří, Eliáš, Pavel, and Ryška, Pavel
- Subjects
- *
WHITE matter (Nerve tissue) , *MAGNETIC resonance imaging , *INTEGRATED software , *SCHIZOPHRENIA , *MAGNETIC resonance - Abstract
Purpose: To assess white matter changes after the first episode of schizophrenia by using fixel-based analysis (FBA). Methods: Diffusion weighted MR images were used to prospectively compare white matter microstructure between subjects after the first episode of schizophrenia (n = 16) and healthy controls (n = 22). The subjects were examined on a 3 Tesla MRI system equipped with a 64-channel head coil. FBA was performed using MRtrix software package (version 3.0.1). Results: A limited area of fibre density decrease was found in the anterior commissure. No fixels of fibre cross-section changes were found. For combined metric of fibre density and cross-section only one statistically significant fixel was found in the right frontal white matter. Conclusion: Using FBA, only a limited area of white matter microstructure corruption was found after the first episode of schizophrenia. Changes were located mainly in the anterior commissure. Compared to other published studies using FBA, the extent of changes is distinctly smaller which can be among other causes subjected to earlier stages of the illness of subjects included in this study. [ABSTRACT FROM AUTHOR]
- Published
- 2022
3. ZMĚNY FRAKČNÍ ANIZOTROPIE BÍLÉ HMOTY MOZKOVÉ U NEMOCNÝCH PO PRVNÍ EPIZODĚ SCHIZOFRENIE.
- Author
-
Slezák, Ondřej, Žižka, Jan, Škoch, Antonín, Bayer, David, Španiel, Filip, Tintěra, Jaroslav, Jandura, Jiří, and Eliáš, Pavel
- Subjects
- *
SCHIZOPHRENIA , *WHITE matter (Nerve tissue) , *BRAIN physiology , *DIFFUSION magnetic resonance imaging - Abstract
Purpose: To assess microstructural changes of the cerebral white matter in the earliest stage of schizophrenia. Methods: Magnetic resonance was used to prospectively compare fractional anisotropy of the white matter between subjects after the first episode of schizophrenia (n = 23) and healthy controls (n = 23). Diffusion tensor data obtained from multidirectional diffusion weighted sequence were analysed by using Tract-Based Spatial Statistics (TBSS). Results: Extensive areas of decreased fractional anisotropy (FA) were found in the white matter after the first episode of schizophrenia, affecting most of the white matter tracts. No areas of significantly increased FA were found when compared to the healthy control group. Conclusion: Extensive areas of microstructural alteration of the white matter are already present during the first episode of schizophrenia. [ABSTRACT FROM AUTHOR]
- Published
- 2018
4. Stiffness anisotropy of Brno Tegel determined by bender elements
- Author
-
Krupička, Martin, Najser, Jan, and Malát, Richard
- Subjects
shear modulus ,brněnský jíl ,smykový modul ,stiffness anisotropy ,Brno clay ,bender elements ,anizotropie tuhosti ,degree of anisotropy ,tégl ,stupeň anizotropie ,tegel ,bender elementy - Abstract
This Thesis deals with the determination of shear moduli of Brno Neogene clay ("tegel") in various directions and the determination of its stiffness anisotropy. The basic measure of stiffness anisotropy in this thesis is considered to be the degree of anisotropy αG given by the ratio of shear moduli in the horizontal (Ghh) and vertical direction (Gvh). Measurements of shear wave velocity were performed on undisturbed vertically and horizontally oriented samples of the Brno tegel in triaxial cell using piezoceramic sensors, so-called bender elements. As an advanced method for determining the degree of anisotropy of the material, another pair of bender elements was used in the measurements, mounted horizontally on the side walls of the sample in the triaxial cell. Based on these measurements, the values of shear moduli Ghh and Gvh for different stress levels were determined. The ratio of shear moduli then determined the degree of anisotropy αG ≈ 1,43 for the given stresses, as the most reliable value based on performed experiments. Literature review part of the thesis briefly summarizes the existing findings from research of physical and mechanical properties of the Brno tegel.
- Published
- 2020
5. Anisotropy of thermal expansion in magnesium materials exhibiting texture
- Author
-
Škraban, Tomáš, Drozd, Zdeněk, and Mathis, Kristián
- Subjects
Anizotropie ,Textura ,Texture ,Thermal expansion ,Magnesium alloys ,Teplotní roztažnost ,Hořčíkové slitiny ,Anisotropy - Abstract
Magnesium alloys are valued for their low density and good mechanical pro- perties. Their characteristic is the tendency to obtain a texture during processing, which together with their hcp crystal structure results in the anisotropy of some physical properties. In this work we examine the effect of the texture on the aniso- tropy of thermal expansion of the widely used AZ31 and ZE10 magnesium alloys. These alloys are in the form of thin rolled sheets and we examine them in an as-recieved state and in a condition after an annealing. The measured samples are cut out of the metal sheet in the direction of rolling and in the perpendicular direction. The measurement is carried out in the temperature range from room temperature to 400 ◦ C. Measuring of the thermal expansion of sheets is problema- tic because they can bend and devalue the measurement results. The result of this work is a confirmation of the existence of this anisotropy and its description. 1
- Published
- 2018
6. Rock strength anisotropy - interpretation of laboratory tests
- Author
-
Vilimová, Anna, Rott, Josef, and Kučera, Petr
- Subjects
tension ,stlačení ,strength ,Hornina ,compression ,anizotropie ,anisotropy ,testing ,Rock ,zkoušení ,pevnost ,tah - Abstract
Anizotropní materiál má v různých směrech různé vlastnosti. Anizotropie pevnosti je zvláštní typ chování pevnosti v závislosti na podobě struktury horniny. Vliv na její velikost má zejména úhel mezi směrem zatížení a plochou oslabení, důležité jsou ale i další parametry jako je tvar a velikost vzorku, vlhkost aj. Podle tvaru této závislosti můžeme anizotropii rozdělit na "U type", "shoulder type" a "undulatory type" nebo ji můžeme členit podle způsobu jejího vzniku na přirozenou a vyvolanou. Pro výpočet pevnosti anizotropních materiálů existuje celá řada vztahů, většina z nich empiricky odvozená z velkého množství laboratorních zkoušek. V současné době nejpoužívanějším a nejkomplexnějším je Hoek-Brownovo kritérium porušení. Nejčastějším způsobem interpretace anizotropie pevnosti je grafické zpracování obálek pevnosti a závislosti napětí při porušení na úhlu mezi směrem zatížení a plochami oslabení. Kombinací těchto dvou grafů je možné vytvořit plochu porušení horniny. Skutečnost, že hornina nemá ve všech směrech stejnou pevnost, a způsob, jak anizotropii charakterizovat a spočítat její velikost, je zásadní zejména pro návrhy geotechnických konstrukcí a určení napěťového stavu horninového masívu.
- Published
- 2018
7. Composite materials and their use in sport
- Author
-
PÍSAČKA, Petr
- Subjects
matrix ,anizotropie ,matrice ,isotropy ,disperze ,dispersion ,izotropie ,composite materials ,kompozitní materiály ,anisotropy - Abstract
This bachelor's study pursues the utilizing of modern composite materials in spor-ting sector. It is processed as an instructional text which could be used as a supportive or supplemental subject matter for materials and technology. The study is divided in two main parts which are further sectioned into subchapters. In the introduction of the first part of the bachelor's study the development of composites is explained during the human history. Following chapter mentions the basic characteristics of the composites and presents various definitions of the composites and the term of synergic phenomenon is clarified. The next chapter discusses the most im-portant matrices based on the plastic materials which are divided into reactoplastic ma-trices and the thermoplastic ones. The features of the particular materials and their use in the production are integral part of this study as well as the illustrative pictures. The second part of this bachelor's work is focused on the practical use in the spor-ting industry namely in sporting aviation, skiing, archery, bicycling, canoeing, soccer and to manufacture hockey sticks. The production, practicability, advantages and the imper-fections are stated here as well. The chapter after that shows the price ranges of the abo-ve mentioned sporting equipment in comparison with the conventional and composite materials. The part of the second chapter is about the future of the composite materials and their current and future utilizing. In connection with the future of the composite mate-rials the use of natural fibers are mentioned too.
- Published
- 2017
8. Study of associated anisotropy decay curves of tryptophan fluorescence of proteins
- Author
-
Pultarová, Martina, Večeř, Jaroslav, and Heřman, Petr
- Subjects
modelování ,tryptofan ,fluorescence ,anizotropie ,anisotropy ,modelling ,doba života ,lifetime ,tryptophan - Abstract
This work focuses on simulation of anisotropy decay curves of a model system where protein P1 with one tryptophan interacts with regulating protein P2 without tryptophan to form a complex P1P2 with simultaneous change of tryptophan fluorescence lifetime of the complex. Under these conditions, the heterogeneous solution of proteins P1 and P1P2 exhibits non- exponential fluorescence anisotropy decay which is deduced also from equations presented in this work. Such curves analytically simulated with and without Poisson noise are the main results of this work. The heterogeneous curves were analyzed using computer programs developed earlier for homogeneous systems. As expected such analysis yields correct values of fluorescence lifetimes but does not recover anisotropy parameters used in simulations. Despite of high intensities of simulated data, anisotropy decay curves of homogeneous solutions are very noisy and can be used only on a relatively short time interval of their decay.
- Published
- 2016
9. Characterization of migmatite fracturing using ultrasonic methods
- Author
-
Petružálek, Matěj, Vilhelm, Jan, Vavryčuk, Václav, and Koktavý, Pavel
- Subjects
acoustic emission ,proces porušování ,migmatit ,fracturing process ,ultrasonic sounding ,migmatite ,anizotropie ,ultrazvukové prozařování ,akustická emise ,anisotropy - Abstract
Submitted PHD thesis is focused on fracturing process of migmatite, which is a low porosity anisotropic rock. Migmatite, from a locality Skalka, was chosen as a suitable experimental material, namely due to its macroscopically visible, plane-parallel structure (foliation). The fracturing was studied by means of uniaxial loading experiments on cylindrical samples with different dip of migmatite foliation: 13ř (subhorizontal), 81ř (subvertical) and oblique (47ř and 67ř). The net of eight piezoceramic transducers was employed for ultrasonic sounding (US) measurement and acoustic emission (AE) monitoring during the loading experiments. Realized study of migmatite fracturing is based on the interpretation of both mentioned ultrasonic methods. Part of this work was a software development, including its testing for processing and interpretation of measured AE and US data. Methodical part of the thesis consists of: development and testing of algorithms for automatic P wave arrival detection; introduction of anisotropic velocity model to describe magnitude and orientation of velocity anisotropy, as well as to localize AE events in anisotropic velocity field; determination of crack initiation stress using first arrival amplitude of US. Based on the interpretation of AE and US data, there was found a...
- Published
- 2015
10. Studium spinové polarizace pomocí laserové spektroskopie
- Author
-
Kuchařík, Jiří, Němec, Petr, and Veis, Martin
- Subjects
Condensed Matter::Materials Science ,Kerr microscopy ,magnetické domény ,magnetic linear dichroism ,magnetická anizotropie ,ferromagnetic semiconductors ,magnetický lineární dichroismus ,magnetic anisotropy ,feromagnetické polovodiče ,kerrovská mikroskopie ,magnetic domains - Abstract
Spintronics is a new branch of electronics, which uses not only the charge of electron but also its spin for transfer and processing of information. For re- al applications it is necessary to understand, how the magnetic state of matter changes not only in time but also in space. This diploma thesis is therefore de- voted to the imaging of magnetic domains in ferromagnetic semiconductors by purely optical methods, which are based on the usage of the magneto-optical ef- fects. In first part of the thesis we concentrated on the optimalization of existing polarizing microscope, whose function is based solely on the polar Kerr effect. After the optimalization we try to use this setup to observe magnetic domains in ferromagnetic semiconductor GaMnAs by the means of the magnetic linear dichroism. 1
- Published
- 2015
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.