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Water soluble cores for aluminum alloys and their influence on the surface quality of castings
Blažík, Petr ; Tomek, Ladislav (referee) ; Kaňa, Václav (advisor)
The goal of this thesis is to examine a possible influence of the water soluble cores on the microstructure of commonly used aluminum alloys AlSi7Mg and AlSi10Mg in the lost wax technology. This thesis only deals with the changes of the eutecticum on the contact surface between the metal and the core and its surroundings where interactions can appear between the core based on the alkali salts NaCl and KCl and the alloy modified by sodium or strontium. The experimental part investigates the influence of the alkali salts on the modification additives and the modification of the structure itself.
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Security of VoIP protocols
Novotný, František ; Číka, Petr (referee) ; Krajsa, Ondřej (advisor)
This bachelor dissertation deals with the VoIP (Voice over Internet Protocol) safety. The most used transport and signal protocols employing this technology are presented first. Two extended protocols, SIP (Session Initiation Protocol) and IAX (Inter-Asterisk eXchange Protocol), as well as open source Asterisk, which is closely connected with these protocols, are shown in detail. After that, methods, attacks and threats able to assure secure transfer in the use of VoIP among users are described. Afterwards the practical part of this essay, divided into two parts, is presented. In the first part, a passive attack in the form of tapping is demonstrated, and in the second, active attacks are described which take the form of forced cancellations and forwarded calls between two communicating users. With both attacks, safety measures that could effectively prevent against their potential attacking are proposed. In the closing part, the VoIP safety is evaluated for securing a quality connection between users communicating through it.
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Study of the effect of metallurgical and technological parameters on mechanical properties of aluminium alloys
Pešek, Jakub ; Krahula, Karel (referee) ; Zemčík, Ladislav (advisor)
Sugested thesis has been made with the intent to observe and describe the length of the modifying effect of three different types of modifiers and their effect on the mechanical properties of aluminium alloy. Next step was to process and evaluate links between mechanical properties and chemical composition. Chemical analysis and mechanical properties of cast samples were obtained. For this purpose and a method of metallographic processing was applied afterwards. The grain size was evaluated before and after the heat treatment. Measurements of the secondary dendrite branches and evaluation of the eutectic morphology were made. The hardness was measured on selected samples.
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Design of winglet for LS-3 glider
Koutník, Tomáš ; Šošovička, Róbert (referee) ; Popela, Robert (advisor)
This diploma thesis describes the design of winglets for LS-3 glider. The method for determination of main winglet parameters based on selected criterion is presented as well as comparation of performace of original wing and final modification. It also includes analysis of wing loading and resetting of speed and weight limits for flying with winglets.
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Thin films modification by focussed ion beam.
Faltýnek, Petr ; Čechal, Jan (advisor)
The purpouse of the master's thesis is study problematic of focused ion beams and their material influence. In this thesis are described interactions in the sample after impact of ion beam, use and applications of FIB systems. Second part of thesis are simulations of ion influence on different kinds of materials by the help of SRIM program.
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Tin dioxide based semiconducting gas sensors
Gablech, Imrich ; Pytlíček, Zdeněk (referee) ; Prášek, Jan (advisor)
This project is aimed at semiconductive gas sensors based on tin dioxide. In the first part, gas sensors are divided depending on their principal of functionality. Next part is about functionality of tin dioxide gas sensors and the possibilities of active layer modification. Experimental describes gas sensor from its drawing until construction, testing and characterization. Several microelectronic technologies such as thin-film, thick-film, LTCC, spray-coating or wire-bonding were used for constructing the sensor. In the last part properties of gas sensors and differences in functionality between modified and unmodified gas sensor are summarized.
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Synthesis of core/shell quantum dots for diagnostics
Mihajlović, Ana ; Vaculovičová, Markéta (referee) ; Pekárková, Jana (advisor)
This thesis deals with biosensors based on modified semiconductor core/shell quantum dots (QDs) for diagnosis. The work is divided into four main parts. The first one discusses the theory required for the use of QDs in bioaplications, there are described methods of synthesis, modification, application and bioconjugation of QDs. In the experimental part, CdTe/ZnS QDs with core/shell structure were prepared, in which the core was modified by MPA, GSH and TGA. In the next step, these QDs were further modified using CDI, EDC and NHS as mediators in order to increase affinity to BSA (bovine serum albumine) and IgG (imunoglobuline G). Prepared conjugates were characterized by fluorescence spectroscopy (Infinite M200Pro, Tecan) and capillary electrophoresis (Agilent 7100).
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Chemical modifications of hydrogels from natural polysaccharide
Poštulková, Hana ; Žídek, Jan (referee) ; Vojtová, Lucy (advisor)
V teoretické části práce by shrnuty chemické a fyzikální vlastnosti, chemická struktura a využití přírodního polysacharidu gum karaya. Hlavním cíle diplomové práce byla alkalická modifikace původní nerozpustné gum karayi na rozpustný produkt, který může být v budoucnu využit pro další aplikace například v medicíně. Nerozpustnost gum karayi je způsobena přítomností acetylových skupin a vícemocných iontů ve struktuře polysacharidu. Byly zkoumány optimální podmínky pro modifikační proces. Pro modifikaci byl použit hydroxid sodný, draselný nebo amonný a čas modifikace od 1 minuty po 24 hodin pro roztok originální gum karayi s koncentrací od 0,1 do 3 %. Pro určení chemického složení originálního a modifikovaných vzorků byla využita FTIR. Bylo prokázáno, že vzorky A2, B1 - 7, C1 - 8 a E1 - 2 byly zcela deacetylovány, protože pás pro acetylovou skupinu nebyl v FTIR spektrech pozorován. Odstranění acetylových skupin alkalickou modifikací bylo taktéž potvrzeno 13C CP MAS NMR. Pomocí XRD byl prokázán amorfní charakter originálního vzorku. Množství vlhkosti a teplotní stabilita vzorků byly zkoumána pomocí TGA. Bylo zjištěno, že termální stability originální gum karayi je vyšší než u modifikovaných vzorků. Termální stabilita modifikovaných vzorků byla ovlivněna reakčními parametry. Entalpické změny vzorků byly studovány pomocí DSC, nicméně nebyly pozorovány žádné významné rozdíly mezi modifikovanými vzorky a originální gum karayou. Prvkové složení bylo určeno pomocí ICP-OES a byla potvrzena přítomnost vápníku, draslíku a hořčíku ve struktuře polysacharidu. Molekulová hmotnost modifikovaných vzorků byla měřena pomocí GPC a byla stanovena na 8 milionů g·mol-1. Reologické měření roztoků gum karayi bylo provedeno pro určení lineární viskoelastické oblasti. Dále byl sledován efekt NaCl na viskozitu originálního vzorku. Viskozita klesala s vyšším množstvím NaCl. Pokles viskozity originálního vzorku je způsoben výměnou vápenatých iontů za sodné, což vede k uvolnění fyzikálně vázané struktury a tím k vyšší rozpustnosti vzorku ve vodě.
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