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Changes in dislocation substructure of S235JR steel during fatigue loading
Jandová, D. ; Gajdoš, Lubomír ; Šperl, Martin ; Kaiser, J.
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and corresponding mean life Nf = 17,950 cycles. The microstructure of the steel consisted of ferrite with a small amount of pearlite. The substructure was observed in as received condition and after application of various relative numbers of cycles n/Nf, these being 0.25, 0.50 and 0.75. An irregular dislocation net occurred in the virgin specimen, however, during cyclic loading the dislocations started to accumulate gradually in slip bands and to form a cell substructure in grains of favourable crystallographic orientations. Total dislocation density, dislocation density in slip bands and inter-band distance were measured using transmission electron microscopy (TEM). The total dislocation density was found to slightly decrease and the density in slip bands to increase with increasing number of cycles. The results concerning the dislocation density were compared with changes in the microplastic limit (MPL) which were determined by the measurement of the inductance of the “specimen - coil” system. They consisted in a rapid initial decrease at the first stage of the fatigue process and in a gradual increase during the major part of the life. These changes can be interpreted on the basis of changes in dislocation density as was verified independently by X-ray diffraction and nanoindentation tests. On the basis of the measurement of dislocation density by TEM it appears that changes in MPL can be connected with the dislocation density in slip bands rather than with the total dislocation density.
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Spermatological characters in Bothriocephalidea (Cestoda)
ŠÍPKOVÁ, Lenka
Spermiogenesis and ultrastructure of the spermatozoon of two bothriocephalidean cestodes, Oncodiscus sauridae and Senga sp., have been studied using transmission electron microscopy. The presence of a classical pattern for spermatological characters (spermiogenesis of type I with dense-material in early stages and sperm of type II with a characteristic ring of cortical microtubules in the anterior part) in Bothriocephalidea is discussed.
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Metoda negativního kontrastu pro diagnostiku virů a bakterií v transmisním elektronovém mikroskopu
ŠOBEROVÁ, Tereza
Bakalářská práce je zaměřena na metodu negativního kontrastu, která se používá pro diagnostiku virů a bakterií v transmisním elektronovém mikroskopu (TEM). V teoretické části je uveden základní popis TEM, metoda negativního kontrastu a základní charakteristika virů použitých pro tuto práci. Hlavní součástí práce je popis postupu, kterým byly preparáty připraveny. Po jejich zobrazení v TEM je popsána kvalita zobrazení virů a porovnání vlivu nejčastějších kontrastních činidel, pH, trehalosy a rozdílných časů kontrastování na zobrazení ultrastruktury biologických preparátů a na velikost jednotlivých virových partikulí. V závěru jsou podle vyhodnocených výsledků vybrána kontrastní činidla zajišťující nejlepší zobrazení objektů a doporučení na možné zlepšení kontrastních vlastností ostatních činidel.
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Prospects of the scanning low energy electron microscopy in materials science
Mikmeková, Šárka ; Hovorka, Miloš ; Konvalina, Ivo ; Müllerová, Ilona ; Frank, Luděk
The use of the scanning low energy electron microscopy (SLEEM) has been slowly making its way into the field of materials science, hampered not by limitations in the technique but rather by the relative scarcity of these instruments in research institutes and laboratories. Various techniques exist which are capable of studying the material microstructure, with the scanning electron microscopy (SEM), (scanning) transmission microscopy ((S)TEM) and focused ion beam (FIB) microscopy being perhaps the most known. A specific way to visualizing the microstructure of materials at high spatial resolution, to achieve a high contrast between grains in polycrystals and very fast data acquisition is to use the cathode lens (CL) mode in SEM. The CL mode in the SEM enables us to detect slow but not only slow, high angle scattered electrons that carry mainly crystallographic contrast based on the electron channeling, mostly in the Mott scattering angular range.
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První zkušenosti s nízkonapěťovým elektronovým mikroskopem
Nebesářová, Jana
Je krátce popsán nízkonapěťový elektronový mikroskop LV EM 5 vyráběný firmou Delong Instruments a jsou prezentovány první zkušenosti s přípravou biologických preparátů pro pozorování v tomto mikroskopu. Je to unikátní přístroj, který je schopen v lékařském a biologickém výzkumu nahradit vysokonapěťový TEM.
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