National Repository of Grey Literature 306 records found  previous11 - 20nextend  jump to record: Search took 0.00 seconds. 
Automation of metallographic sample cleaning process
Čermák, Jan ; Ambrož, Ondřej ; Jozefovič, Patrik ; Mikmeková, Šárka
Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual sample handling. An etchant or electrolyte results in inhomogeneous surface quality because the solution runs off the specimen surface during its removal from the beaker. High-quality specimen cleaning is absolutely crucial for the acquisition of the specimen suitable for characterization by a scanning electron microscope operated at very low landing energies of the primary electrons (SLEEM). The SLEEM technique is a powerful tool for the characterization of advanced steels, as described by many scientific papers. The SLEEM requires the specimen absolutely free of water and any organic residues on the surface. This work presents a novel unique apparatus enabling automatic specimen cleaning and drying after the etching or electropolishing processes. Automation reduces the influence of dependent variables that would be introduced into the process by the metallographer. These variables include cleaning time, kinematics, and motion dynamics, but the process can also be affected by variables that are not obvious. Performed experiments clearly demonstrate our in-house designed apparatus as a useful tool improving efficiency and consistency of the sample cleaning process. The high quality of the specimen surface is verified using a light optical microscope, an electron scanning microscope, and above mentioned SLEEM technique.
TCO work function tuning by nanodiamonds
Čermák, Jan ; Miliaieva, Daria ; Sokeng-Djoumessi, A. ; Hoppe, H. ; Stehlík, Štěpán
Deposition of nanodiamonds is found to be able to adjust the work function of transparent conductive oxides that are commonly used in photovoltaics. It also turned out that the change is dependent on the nanodiamond surface termination and that it is not stable in time.
New methods of sample preparation for modern scanning electron microscopy
Ambrož, Ondřej ; Čermák, Jan ; Mikmeková, Šárka
Modern scanning electron microscopes (SEM) are equipped with a very sophisticated detection system that allows the detection of signal electrons by several differently located detectors simultaneously. Signal electrons are filtered according to energy and angle. Effective signal filtering in SEM together with the possibility of using very low impact energies of the primary beam leads to the extreme sensitivity of this method to the quality of the sample surface. Current metallographic methods of sample preparation are becoming insufficient for advanced imaging in modern SEM instruments. Classical sample preparation proves to be completely unsuitable especially for low-voltage scanning electron microscopy. The work will present the first results of the influence of preparation methods on the surface condition and the possibility of differentiating the individual phases of TRIP steel using advanced electron microscopy techniques. The possibilities of new procedures using robotics will be shown.
Apparatus for automatic chemical etching of metallographic samples
Ambrož, Ondřej ; Čermák, Jan ; Mikmeková, Šárka
The microstructure of steels after mechanical polishing is revealed only by the application of a suitable etchant. To achieve adequate optical or electron microscope images, the specimen surface must be free of any artifacts. Chemical etching can be defined as a controlled corrosion process. The metal of the investigated material passes as cations into the etchant solution during the chemical etching reaction. Chemical etching is usually performed manually either by immersing the sample in the etchant with simultaneous stirring or by swabbing with a lint-free cloth soaked in the etchant. It is also extremely important to debug the process of removing the sample from the bath and subsequent cleaning. It is recommended to wash the sample after removal from the etchant with water (distilled or demineralized) or alcohol (ethanol, methanol, or isopropyl alcohol) and dry it properly (depending on the etchant and the etched material). The main problem with these processes is the human factor, which significantly contributes to the already limited repeatability. All operation steps must be performed by properly trained personnel in the field of occupational safety because hazardous substances are handled. A high manual dexterity is also needed. Training a new employee is a long-term process. Moreover, keeping the exact etching time can be a challenge and one second can decide success. These problems become more serious in the case of using surface sensitive analytical method, such as a low energy scanning electron microscopy, due to the high spatial resolution and extreme surface sensitivity. We have developed an apparatus for automatic etching of metallographic samples of purpose to overcome all above-mentioned difficulties. The apparatus and results of the first experiments will be presented.
Old English and Danish: A Structural Comparison
Ambrožová, Alžběta ; Čermák, Jan (advisor) ; Fúsik, Ondřej (referee)
The aim of the bachelor thesis is to compare Present-Day Danish and Old English, classify them from the point of view of morphological typology, and discuss some of their basic linguistic features, taking the history of both languages into account. The focus of the thesis will be a comparison according to the typology of the Prague School: the text will be structured on the basis of a typological scheme by František Čermák. Old English was not so strongly influenced by Latin, and its relationship with other Germanic languages, including Danish, is therefore much more visible than in Present-Day English. Vocabulary is the most prominent feature that the two languages have in common. On the other hand, there are significant differences between them in terms of morphological typology. Compared to Present-Day English, Old English was significantly more inflected, while Present-Day Danish is primarily isolating with some agglutinative elements. The objective of the thesis is to discuss the historical context in which both languages developed and show some of the typical features that they share. In the analytical part, specific examples of typological features will be discussed, and on their basis the overall character of both languages and their similarities and differences will be evaluated.
Proposal warehouse in engineering company
Čermák, Jan ; Císařová, Michaela (referee) ; Štroner, Marek (advisor)
This master thesis deals with the design of a new warehouse of an input material in an unnamed engineering company. The main intention is to create a well arranged and functional storage of metal sheets, tubes, HSS profiles and HEB profiles. The first part of the thesis includes a theoretical introduction to the problematics of storage, then the thesis deals with the analysis of the current state of production and storage in the company. The warehouse design is made with the data about material consumption in 2021. In total, two variants of the warehouse solutions were designed. The difference is in the location of the warehouse and in the handling equipment, that was used. Forklift trucks are used in the first variant and crane handling is in the second. Disposition of the warehouse was solved based on the condition analysis, provided data, and performed calculations for the target year 2023. In conclusion was performed a technical and economical evaluation of the proposals, where both variants were compared. The warehouse design is supplemented by the drawing documentation of both solution variants.
The effect of surface roughness on friction and lubrication in simulated gear contact
Mořický, Ondřej ; Čermák, Jan (referee) ; Šperka, Petr (advisor)
This diploma thesis deals with experimental study of the effect of surface roughness on lubricating film formation and friction behaviour in lubricated point contact. The ball-on-disc contact is operated under conditions of transition from mixed to elastohydrodynamic lubrication regime. The measurement of the thickness of thin lubrication films on generally rough surfaces is approached by fluorescence microscopy. The effects of magnitude and character of the initial roughness, including their evolution during the running-in processes, are described. The result is a closer understanding of the mechanisms taking place in this type of contact and the identification of the optimum surface roughness in terms of resistance to changes during running-in for specific operating conditions.
Grease lubrication in rolling element bearings
Kroupa, Jiří ; Čermák, Jan (referee) ; Frýza, Josef (advisor)
This diploma thesis deals with an analysis of lubrication film in contacts of simulated thrust ball bearing lubricated by greases and comparison of the film thickness between this apparatus and ball-on-disc. According to the literature, ball-on-disc is the most used apparatus for studies of EHL. But these devices neglect some important factors acting in real bearing such as presence of cage, number of rolling elements, their spin or a type of contact geometry. Therefore it is necessary to investigate comparability of these approaches. For this purpose, measurements on unique apparatus of simulated thrust ball bearing are performed. The effect of each factor is evaluated employing Factorial design method. Significant differences are discovered between results, primarily in tendency of contacts to starvation. According to these results, it is necessary to focus the research in the field of bearing lubrication on conditions closer to real bearings.
Advanced epidemic models and their analysis
Skácelová, Radka ; Šremr, Jiří (referee) ; Čermák, Jan (advisor)
This diploma thesis analyzes several SIR epidemiological models which are described by a system of non-linear differental equations; it is mainly focused on SIR models with biths and deaths describing long-term epidemics. The goal of this thesis is to develop and analyze models with a time delay, and to extend some of the studied models using the graph theory, find their stationary states and analyze their stability. The thesis is particularly focused on spatially heterogenous stationary states for special types of graphs - complete graphs, stars and cycles.
Analysis of Some Evasion and Pursuit Strategies
Barusová, Ema ; Hoderová, Jana (referee) ; Čermák, Jan (advisor)
The main objective of this bachelor's thesis is an analysis of chosen pursuit and evasion problems. It puts great emphasis on formulation of the mathematical model followed by its analysis, which usually leads to an analytical solution.

National Repository of Grey Literature : 306 records found   previous11 - 20nextend  jump to record:
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