National Repository of Grey Literature 171 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Plasma diagnostics for the therapeutic applications
Kletzander, Lukáš ; Slavíček, Pavel (referee) ; Krčma, František (advisor)
Plasma, an ionized gas, is often regarded as the fourth state of matter. It has many useful applications, from arc welding to plasma displays. An emerging application of low-temperature plasma is in medicine, too. Reactive species generated in plasma discharges are the source of its usefulness in sterilization and supporting would healing. The detailed characterization of plasma is a key point before its real application in medicine. Thus, this is the main goal of this thesis. The subject of this thesis was the characterization of three new experimental applicators generating microwave plasma at 2,45 GHz in argon. The angle of argon flow into the applicator was the differentiating factor, the three versions have had angles of 0, 15 and 30 degrees. This angle affected the spatial distribution of the generated reactive species, as well as the discharge length and its stability. The reactive species, which included nitric oxide, oxygen radical and hydroxyl radical, were analyzed using optical emission spectroscopy. The diagnostic was done along the discharge axis for different mass flows of argon and at different power. In addition, photos of the discharges at selected powers and argon flows were taken. The lengths of the discharges were measured from the images. It was found out that the intensity of spectral transitions of the reactive species is dependent on the aforementioned parameters – mass flow of argon and supplied power. The intensity of these particles’ radiation related to their concentrations generally increased as more power was supplied to the applicator. The intensity subsequently decreased with increasing gas flow. The active region of the discharge also decreased as gas flow was increased. The length of the discharges was also dependent on supplied power and gas flow. The three versions of the applicators have shown differences – a maximum and a subsequent decrease in length with increasing gas flow were observed, the rate of the decrease being different for the three versions. The average length of the discharge was also different for the three applicators.
Study of the Influence of Faradaic Processes on the Efficiency of Yeast Electroporation
Martinů, Dominik ; Krčma, František (referee) ; Ehlich, Jiří (advisor)
Electroporation is a widely used method in biotechnology and healthcare. It involves the application of short, intense electric pulses, which create pores in the cell membrane. These pores allow the exchange of molecules between the electrolyte and the intracellular environment. Although electroporation is a standard technique, its exact mechanism remains unknown and is the subject of current research. It is assumed that the primary mechanism of electroporation is the effect of the electric field itself. Recent studies, however, suggest that one of the accompanying mechanisms may also be the effect of reactive oxygen species (ROS) and generally the products of faradaic processes. These highly oxidizing molecules can influence both the efficiency of electroporation and cell viability. The hypothesis was that by anodizing electroporation electrodes, i.e., creating a thin dielectric layer on their surface, the production of ROS can be prevented. By subsequently comparing the efficiency of electroporation using prepared capacitive electrodes and classic faradaic electrodes, it would be possible to reveal the effect of ROS on electroporation. The production of H2O2, as a representative of ROS, was mapped using standard electroporation buffers, protocols, and various electrode materials. The concentration of H2O2 was determined spectrophotometrically by its reaction with 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by horseradish peroxidase (HRP). Electrodes were selected to achieve low, medium, and high production of H2O2. These selected electrodes were used for in vitro electroporation of Saccharomyces cerevisiae yeast, with the efficiency of permeabilization determined by electrochemical impedance spectroscopy (EIS) and fluorescence measurement of propidium iodide (PI) intake. It was found that the action of ROS is not the primary mechanism of pore formation in the cell membrane during electroporation and does not significantly affect the efficiency of this method. However, the results do not exclude their role in secondary processes that affect the kinetics of pore closure and cell viability after electroporation.
Study of electrical discharge initiated chemical processes in Titan like atmosphere in stationary regime
Zbytek, Filip ; Chudják, Stanislav (referee) ; Krčma, František (advisor)
The aim of the presented bachelor's thesis was the study of chemical processes initiated by electric discharge in an atmosphere similar to that of Titan. This bachelor's thesis focuses on simulating Titan's atmosphere at normal laboratory temperature and atmospheric pressure. Titan's atmosphere is mainly composed of nitrogen, which constitutes 98 % of the atmosphere. For the simulation, spark and glow electric discharges generated in a special reactor were used. Measurements were conducted with varying CH4 flow rates of 0, 1, 2, 3, and 4 sccm. The first part of the measurements was conducted for the spark discharge and the second part for the glow discharge, both under the same conditions. The synthesized gaseous products were analyzed using proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). Mainly simple nitrogenous aliphatic hydrocarbons were detected, but with increasing CH4 flow, the formation of more complex aromatic hydrocarbons occurred for both discharges. The composition of the plasma and its diagnostics were investigated using optical emission spectrometry (OES). Measurements using proton transfer reaction mass spectrometry and optical emission spectrometry were conducted simultaneously.
LIBS detection of trace elements in polymeric matrice
Kočenda, Dominik ; Kopřivová, Hana (referee) ; Krčma, František (advisor)
When recycling plastic materials, it is important to determine whether they contain concentrations of hazardous impurities, such as heavy metals, above permissible limits. This bachelor's thesis focuses on quantifying cadmium in a polymer matrix using Laser-Induced Breakdown Spectroscopy (LIBS). Samples of polypropylene and polystyrene with unknown cadmium concentrations were examined. Calibration samples for both types of polymers were prepared for quantification and then analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) in an external laboratory. These results were used as calibration values for the LIBS method and also to verify the accuracy of the obtained results. Calibration curves for cadmium were created from the calibration samples, which enabled the determination of unknown cadmium concentrations in the polypropylene and polystyrene samples and the determination of the detection limit of cadmium using the LIBS method. Cadmium in the unknown samples was quantified with an average accuracy of 90 % and precision of 85 %.
Detection of aromatic compounds in plants
Tilešová, Kristína ; Zlámalová Gargošová, Helena (referee) ; Krčma, František (advisor)
This bachelor thesis is focused on the detection of aromatic compounds in plants. Selected plant was Celery (Apium graveolens). In the theoretical part, methods for the volatile substances analysis were reviewed. In the experimental part, celery sample was converted from solid to liquid form and then analyzed using proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) and gas chromatography-mass spectrometry (GC/MS). Aromatic compounds with a stronger signal were selected using PTR-TOF-MS, which were analyzed and identified using GC/MS. Monoterpenes represented the main group of compounds in celery seed essential oil, the most important is D-Limonene. Celery also contains phthalides, aldehydes, alcohols, esters. Using a combination of PTR-TOF-MS and GC/MS was obtained the quantitative and qualitative composition of celery essential oil.
Studz of direct and indirect plasma application on onion seeding bulbs
Krejsová, Lenka ; Enev, Vojtěch (referee) ; Krčma, František (advisor)
Nowadays, agriculture is based on conventional methods that involve the application of pesticides, agricultural chemicals and fertilizers. These substances have a negative impact on nature and human health, so more environmentally friendly methods are being sought. This thesis deals with the analysis of fragrances in onions treated with plasma before planting. The treatment was carried out to see if it would improve onion growth while maintaining or increasing the fragrance content. The theoretical part deals with the soil and it is characterization methods, plasma, quantitative and qualitative methods for the determination of volatile substances. It contains the principles of UV-VIS spectrometry, atomic absorption spectrometry (AAS), mass spectrometry (MS) as well as tandem connection of gas chromatography with mass spectrometry (GC–MS). The experimental part was carried out over a period of three years at 22 sites. The preparation and analysis of soil samples are described, which was also evaluated. Furthermore, the procedures for treating the bulbs with corona discharge and plasma-activated water before planting were described. In total, four treatment variants were carried out and bulbs from the fifth variant were not additionally treated. Each treatment variant was planted in four replications of ten bulbs each. Twenty selected grown onions from one site were individually converted to liquid samples and the saturated vapor was analysed by proton transfer reaction time of flight mass spectrometry (PTR–TOF–MS). Thanks to this analysis, the concentrations of volatile substances were determined. Some samples were analyzed by gas chromatography with mass spectrometer as detector to identify the compounds. Subsequently, the data were processed and evaluated. From the results obtained, it is evident that plasma treatment can be useful for the treatment of onions in agriculture, because it confirmed harvest increase without decrease of fragrances concentrations. Thus, it is necessary to carry out experiments on a larger scale in the future.
Surface cleaning of archaeological objects by plasma generated in water solutions
Tihonová, Jitka ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
This bachelor thesis is focused on the plasma surface treatment of historical ceramics by low temperature electrical discharges in water solution. Four samples were chosen - two of the Lusatian Urnfields Culture and two of Anabaptist Faience. The treatment was done at minimum power of the power supply. Stainless steel electrode and a specially designed electrode system with wolfram wire in the quartz glass capillary were used for generation of discharge using an audio frequency power supply. Elemental analysis by scanning electron microscopy (SEM) was done before and after the treatment and values were compared with the elemental analysis of material’s core. Samples of the Lusatian Urnfields Culture were successfully treated without any surface damage. The first one of samples of Anabaptist Faience was damaged. The experiment was repeated on the glass to determine the cause. It was find out that damage was probably caused by thermal stress. The second one of Anabaptist Faience was already treated without damage. Next research will be focused on determining specific conditions of the power supply, modification of water solution and modification of sample’s surface for the most efficient ancient ceramics cleaning.
Influence of metallic atoms on nitrogen post-discharge
Bocková, Ivana ; Kudrle, Vít (referee) ; Krčma, František (advisor)
The aim of this master thesis is to study the influence of metallic atoms on nitrogen post-discharge. Pure nitrogen post-discharge is a subject study of many works dealing with kinetic processes in plasma. Unfortunately, there are only a few published works that present influence of various traces on nitrogen post-discharge kinetics. This master thesis deals with problems of nitrogen post-discharge containing mercury traces. All experimental data were obtained using optical emission spectroscopy of a DC discharge in a flowing mode, which can achieve appropriate temporal resolution in the order of milliseconds. Spectra emitted during the post-discharge were recorded in the range of 320-780 nm and the following molecular spectral systems were identified: • 1. positive system of nitrogen: N2(B) -> N2(A), • 2. positive system of nitrogen: N2(C) -> N2(B), • 1. negative system of nitrogen: N2+(C) -> N2+(X), • NO-beta system: NO(B) -> NO(X). Besides them we were able to record the mercury line at 254 nm, only (in the spectrum of the first as well as in the second order); no other mercury lines were observed. The mercury vapor was introduced into the system at selected post-discharge time. Dependence of selected molecular band head intensities as well as mercury line intensity on experimental conditions (pressure, discharge power, wall temperature, time of mercury vapor introduction) were observed in time evaluation. The data obtained in pure nitrogen were used as a reference. The obtained results showed very high sensitivity of kinetic processes on mercury atoms presence. If mercury was introduced into the post-discharge the mercury line was observable around the site where mercury vapor was introduced into the discharge. The experimental data showed that mercury line intensity was directly proportional to the mercury atoms concentration and saturation effect could be observed. The energy level diagram demonstrates that the observed mercury line can be excited by collisions with nitrogen ground state molecule excited to vibrational level 18. Thus the mercury can be used for the monitoring of population at this vibrational level. Finally we obtained the population profile at this nitrogen metastable level during the post-discharge. The presented work demonstrates possibility of mercury atoms application for the monitoring of one nitrogen metastable state. Unfortunately, the contemporary data are not sufficient for the measurement of metastable absolute concentration. However, complex understanding of nitrogen post-discharge kinetics is still an open problem. Therefore a lot of future work should be done although the presented work brings a good fundament for such research.
Study of electrolyte influence on diaphragm discharge stability and efficiency
Němcová, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
This thesis is focused on so-called diaphragm discharge, which is one kind of electric discharges in liquid, which belongs among so-called AOP´s techniques, still more used for water cleaning in the present. One of effectiveness and stability indicators of diaphragm discharge is generation of hydrogen peroxide. In theoretical part, detail principle description of electric discharge in liquid is situated. Further, properties of electrolyte are introduced and general spectrophotometric method of obtained sample determination is described. In experimental part, a full procedure of experiment is introduced. Next part containing results and discussions introduces particular results of individual measurements and their reasons. Final chapter is the end, which forms total summary and evaluation of all results. By the application of all chosen electrolytes in solution at diaphragm discharge formation of hydrogen peroxide has appeared. Inorganic and organic electrolytes were used. As inorganic electrolytes following salts were selected – solutions of halogenides, next sodium nitrate as a representative of nitrates, potassium dihydrogenphosphate as a representative of phosphates, etc. Representative of organic electrolytes was citric acid. The value of initial conductivity of electrolytes had the main influence on hydrogen peroxide formation. Electrolytes potassium dihydrogenphosphate and sodium sulphate the great influence on effectiveness and stability of the diaphragm discharge. Their rate constants reached maximum value by the application of solution with initial conductivity of approximately 400 mikrosiemens, particularly 0.0492 mmol/l.min and 0.048 mmol/l.min. On the contrary, low values of rate constant were achieved in electrolyte ammonium chloride at around the same initial conductivity – 0.0269 mmol/l.min. During experiments stainless steel and platinum electrodes were used. It was found that kind of electrode material hadn’t influence on generation of hydrogen peroxide. Hydrogen peroxide was formed only in the cathode space.
Study of plasmachemical reduction of corrosive layers on brass
Řádková, Lucie ; Selucká, Alena (referee) ; Krčma, František (advisor)
The main topic of this bachelor thesis is plasmachemical treatment of archeological artifacts, especially plasma chemical treatment of brass corrosion layers. Low-pressure, low-temperature hydrogen plasma is used for this process. Nowadays, the technology is used mainly for iron or silver based materials but even for them the optimal conditions for the corrosion removal are not fully known yet. The knowledge about other metallic materials is fully missing. Two sets of brass samples were prepared in different corrosion atmospheres. The first atmosphere was prepared using saturated vapors of HCl. The samples were in this atmosphere during one month, and corrosion layers were orange-brown. The second set was prepared using ammonium solution, the samples were in this atmosphere for one day, corrosion layers were blue. The generation of capacitively coupled plasma in continuous mode by different supplied power was done. The experiments were carried out at 100 Pa with hydrogen gas flow of 50 sccm. Discharge power was varied in the interval 50 – 200 W and the treatment duration was 70 – 140 min. The optical emission spectroscopy of OH radical was used to find out all changes those have been resulting from plasmachemical reactions. The OH radical integral intensities were observed, they were used to monitoring plasma chemical reduction process. Spectral intensity of spectroscope was in the range 290 – 330 nm. After the plasmachemical treatment, it was very difficult to remove corrosion layers of HCl, but removing of NH3 corrosion layers was easy. It was caused by type of corrosion process (corrosion layers were influenced by time of corrosion process). This bachelor thesis is the start to find out conduct corrosion layers of brass in plasma treatment. In future, plasma treatment could be used to treatment of real archaeological artifacts.

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