|
|
Function of Magnesium Ions in the Formation of Biologically-Active Nucleic Acids Structures
Espinoza Herrera, Shirly Josefina ; Štěpánek, Josef (advisor) ; Mašek, Vlastimil (referee) ; Setnička, Vladimír (referee)
ESPINOZA HERRERA S.J. - DOCTORAL THESIS - FUNCTION OF MAGNESIUM IONS IN THE FORMATION OF BIOLOGICALLY-ACTIVE NUCLEIC ACIDS STRUCTURES ____________________________________________________________________ ABSTRACT Interaction of magnesium ions, the divalent ions with the highest concentration inside living cells, with the key biomolecules of nucleic acids was studied with aim to find out structural details of the interaction mechanism and effect of the magnesium ions presence on the nucleic-acid structure and structural transitions. Raman spectroscopy was chosen as the main experimental method, some complementary measurements of UV absorption spectra were also performed. Basic analyses of the spectral series obtained as a function of temperature and/or for various concentrations of Mg2+ ions were done by means of factor analysis. Where possible the factor analysis outputs were used for fits of appropriate thermodynamic equations. For the studies, various nucleic-acid molecular models were employed, in particular complementary RNA homopolynucleotides polyA and polyU, DNA homopolynucleotides polydA and polydT and RNA 14-mer oligonucleotide representing the apical hairpin of the TAR segment of HIV-1 genomic RNA. We have confirmed via Raman spectroscopy that magnesium ions added to a solution of polyA-polyU...
|
|
|
Effect of composition and microstructure on mechanical and corrosion properties in magnesium alloys with a potential for medical applications.
Minárik, Peter ; Král, Robert (advisor) ; Chráska, Pavel (referee) ; Landa, Michal (referee)
Title: Effect of composition and microstructure on mechanical and corrosion properties in magnesium alloys with a potential for medical applications. Author: RNDr. Peter MINÁRIK Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. Dr. rer. nat. Robert Král, PhD., Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Doctoral thesis is focused on the effect of thermomechanical processing through ECAP on the microstructure, mechanical properties and corrosion properties. The investigation was performed on the extruded magnesium alloys AE21, AE42 and LAE442, because their potential for medical applications. Microstructure development was characterized in detail by scanning electron microscopy together with detection of back scattered electros, transmission electron microscopy and positron annihilation spectroscopy. Development of mechanical properties was investigated by tensile and compression deformation tests and microhardness measurement. Corrosion resistance was investigated by linear polarization method. Fine-grain structure with grain boundaries with high angle misorientation was achieved by the thermomechanical processing. The resulting...
|
|
|
Biodegradable Mg-based materials for stents and bone implants
Zemková, Mária ; Král, Robert (advisor) ; Stráská, Jitka (referee)
The bachelor thesis is focused on the effect of mechanical processing rotary swaging (RS), specifically on the microstructure, mechanical properties and corrosion properties. The investigation was performed on the magnesium alloy AE42 with a different number of RS passes, which can be useful for medical applications. RS is more efficient and cheaper alternative to different material processing methods producing fine-grained struc- ture. Fine-grain structure with grain boundaries with high angle misorientation was achieved by this process. Microstructure was inhomogeneous - the grain size decreased from the surface to the center. An improvement of mechanical properties with the increase in the number of swaging steps was observed. Processing also led to a decrease in corrosion resistance in this alloy. Microstructure development was investigated by electron microscopy scanning. Development of mechanical properties was characterized by compression deformation tests and microhardness measurements. Linear pola- rization method was used for the interpretation of corrosion resistance. 1
|
|
|
Study of deformation processes in hexagonal materials
Čapek, Jan ; Mathis, Kristián (advisor) ; Karlík, Miroslav (referee)
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation.
|
|
| |
|
|
Study of phytic acid-based organic conversion coatings on magnesium alloys
Zbíral, Roman ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
This thesis deals with organic conversion coatings based on phytic acid, on the magnesium alloys. In theoretical part it deals with corrosion properties of magnesium and magnesium alloys, usage of magnesium alloys for biomedicine applications. There are also summarized information’s about usage of phytic acid, it’s reactions with magnesium and magnesium alloys. At the end of theoretical part is search about phytic acid conversion coatings deposited on magnesium alloys. There are studied optimal conditions for application of phytic acid coatings such as pH, concentration, time of deposition, etc. Based on the knowledge from the theoretical part, a layer based on phytic acid was deposited on the surface of Mg alloy AZ31. The coating was evaluated in the experimental part in terms of its morphology and structure, chemical and corrosion behaviour. Scanning electron microscope (SEM) images showed the presence of microcracks in the dried coating. The chemical nature of the phytic acid-based conversion coating was investigated by energy dispersive spectroscopy (EDS) techniques in combination with Fourier transform infrared spectroscopy (FTIR). The electrochemical corrosion behaviour of Mg alloy AZ31 and coated Mg alloy was investigated by potentiodynamic polarization in Hank's solutions. Based on the obtained values of the corrosion potential and the corrosion current density, it can be stated that the applied layer of the conversion coating leads to an improvement of the corrosion properties. From the results of SEM analysis of samples after exposure in a corrosive environment, it was found that during potentiodynamic measurements no significant manifestation of corrosion attack was observed in coated samples, as was the case with Mg alloy AZ31.
|
|
|
Fluoride conversion coatings on composite Mg/MgO materials
Peroutka, Jakub ; Buchtík, Martin (referee) ; Hasoňová, Michaela (advisor)
Bachelor thesis deals with preparation of composite materials based on Mg/MgO and their subsequent coating with fluoride conversion coating. Materials based on Mg/MgO were prepared by powder metallurgy. The theoretical part contains of basic magnesium information, advantages and disadvantages of Mg and brief Mg preparation. In the next part there are summarized basic principles, advantages and disadvantages in powder metallurgy. The second theoretical part deals with basic properties of MgO, literary research which deals with description of MgO on chemical structure of different varieties of Mg alloys or composition materials based on Mg/MgO. The last part of theoretical part describes conversion coatings, brief description of chemical reaction kinetics and diffusion of fluoride conversion coating. The experimental part deals with preparation of composite materials based on Mg/MgO by powder metallurgy. The main goal of experimental part was description of possible effect of MgO content on the formation of fluoride conversion coating.
|
|
|
Fitness center clients nutrition focused on protein and magnesium intake
Pajič, Barbora ; Vilikus, Zdeněk (advisor) ; Petráková Doležalová, Radka (referee)
The diploma thesis deals with the importance of protein and magnesium in the diet of recreational visitors to fitness centers. Excessive protein intake at the expense of other macronutrients is a very common phenomenon in the fitness sector. Magnesium is an important element for muscle regeneration and its deficiency can have a negative effect on weight reduction and muscle gain, leading to fatigue and cramps, which many athletes encounter. As visits to the fitness center become more and more popular nowadays, it is important that athletes are not subject to misleading and confusing information from the internet and look for proven sources. The aim of the diploma thesis was to compare eating habits, especially protein and magnesium intake, in two groups of people divided according to the frequency of training in the fitness center. This work is divided into theoretical and practical part. The theoretical part deals with nutrition in the fitness industry in general, but more attention is focused on proteins and magnesium. Quantitative research using a questionnaire survey was chosen for the practical part of the work. A total of 30 respondents participated in the research, divided into two groups - athletes and non-athletes. Non-athletes were considered to be those who have two or fewer workouts per...
|
|
|
Modification of graphitic cast irons and fading of the modification effect
Paták, Daniel ; Bořil, Petr (referee) ; Kaňa, Václav (advisor)
The thesis presents a literature research concerning the production of cast irons with globular graphite. Emphasis is on the clarification of the modification principle and the fading of modification effect. Within the scope of the thesis, an in-house experiment investigating the issue has been carried out with a description of the modification method itself and an evaluation of the decay of the modification effect.
|
|
|
Structure and mechanical properties of magnesium materials prepared by SPS
Pleskalová, Kateřina ; Hutařová, Simona (referee) ; Doležal, Pavel (advisor)
This diploma thesis deals with the processing of the magnesium-based powder materials with the addition of zinc by the spark plasma sintering. The aim of this thesis is to evaluate influence of sintering parameters and zinc content on the microstructure and mechanical properties of the material. First part of the thesis is literary research which is divided into two main chapters. The first chapter describes magnesium-based materials and mentions their use as biomaterials. The second chapter discusses powder metallurgy, specifically magnesium powders and spark plasma sintering. In the experimental part the powders were sintered at temperatures 300 °C and 400 °C and an analysis was performed using optical microscope, scanning electron microscope, then also EDS analysis and hardness, microhardness and three-point bending tests were performed. An increase in hardness was observed with increasing zinc content and with increasing sintering temperature. The flexural strength was higher for materials sintered at a temperature of 400 ° C.
|
guest ::
