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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Model and Validation of Static and Dynamic Behavior of Passive Diamagnetic Levitation for Energy Harvesting

Siyambalapitiya, Chamila Shyamalee 01 January 2012 (has links)
This dissertation reports the investigation conducted on the static and dynamic behavior of the passive diamagnetic levitation systems. Attachment of a device to a substrate hinders the optimum performance ability of vibrating devices by altering the dynamic behavior of the moving part whilst introducing higher overall stiffness. The significance of this effect is prominent especially in vibration based energy harvesters as higher stiffness elevates the resonance frequency of the system, making it difficult to tune into ambient low frequencies. Other advantages of the proposed method are given by the removal of mechanical bending elements, which are often the source of energy dissipation through thermo-elastic damping and affects device reliability and durability. In this research, diamagnetically levitated resonators that can be utilized in energy harvesting were proposed and investigated as a possible solution to overcome these problems. Permanent magnets in an opposite neighboring poles (ONP) configuration were used to provide the magnetic field required for levitation. Pyrolytic graphite (PG), which is the known highest diamagnetic material, serves as the levitating proof mass. Experimental results show that the static levitation height has a linear dependence on the thickness and a nonlinear dependence on the area of the levitating proof mass that can be approximated to a third order polynomial equation. Also, the study proved that a thinner proof mass provides a higher air gap while length of the proof mass beyond a certain value (l >10 mm for the experimental system considered in this dissertation) has no significant effect on increasing the air gap. It was also observed that levitation can slightly increase by attaching magnets to a sheet of steel (ferromagnetic material). To the best of my knowledge, this dissertation is the first to address the parameterized studies in the dynamics of diamagnetic levitated objects by permanent magnets. Measurements performed on a diamagnetic levitating prototype system show that the resonance frequencies are lowered by approximately 3- 4 orders of magnitude in levitated systems compared to the attached systems demonstrating the feasibility of using levitating techniques for micro to meso scale energy harvester applications. Also, there is a significant dissimilarity observed in this study compared to the mechanically attached systems: The resonance frequency has a dependence on magnetic field strength, and is shifting towards lower values when increasing the strength of the magnetic field. This indicates that the virtual spring of a levitated proof mass is not a constant and therefore, the resonance frequency of the diamagnetic levitated systems is able to be fine-tuned by varying the magnetic field. Finite Element Method (FEM) models were developed using COMSOL software that can simulate 3D magnetic flux formation of an array of permanent magnets and the diamagnetic levitation. The appropriate magnetic force equation from the two force equations that exist in the literature was established for the static levitation with the help of experimental and simulation results. Moreover, these models are able to provide the magnetic force exerted on diamagnetic objects at different heights, stable levitation height and position and also an indication of the maximum stably levitated size of the diamagnetic material. Future endeavor of this study is to realize the diamagnetic levitation in energy harvesters. The results obtained from this research will not be limited to harvester applications but will also be beneficial to other diamagnetic levitation related systems, as these parameters are fundamental and necessary for the foundation of the research in the field of interest.
2

Electrocatalysis of degradation products of V-type nerve agents at single-walled carbon nanotube basal plane pyrolytic graphite modified electrodes

Pillay, Jeseelan 24 April 2008 (has links)
O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX) and O-isobutyl-S-2-diethylaminoethyl methylphosphonothioate (R-VX), are considered chemical warfare agents due to their strong acetylcholinesterase-inhibiting properties. Subsequent to terrorist use of these V-type nerve agents in both Japan and the United States of America (the September 11, 2001 attacks) and the limited capability of anti-terrorist groups to detect such weapons, there has been an increased obligation by the Chemical Weapons Convection for specific detection and identification methods for VX and R-VX. Chemical and/or enzymatic hydrolysis yields sulfhydryl mimic products, diethylaminoethanethiol (DEAET) and dimethylaminoethanethiol (DMAET). This thesis investigates the electrocatalytic parameters of DEAET and DMAET using basal plane pyrolytic graphite electrodes (BPPGEs) modified with: (a) single-wall carbon nanotube (BPPGE-SWCNT); (b) SWCNT functionalised with cobalt (II) tetra-aminophthalocyanine by (i) physical (BPPGE-SWCNT-CoTAPc(mix)), (ii) chemical (BPPGE-SWCNT-CoTAPc(cov)) and (iii) electrochemical adsorption (BPPGE-SWCNT-CoTAPc(ads)) processes; (c) nickel powder (BPPGE-Ni); (d) BPPGE-Ni decorated with SWCNT (BPPGE-Ni-SWCNT), and (e) SWCNT functionalised with nickel (II) tetra-aminophthalocyanine (BPPGE-SWCNT-poly-NiTAPc). Electrochemical studies (performed by voltammetric and electrochemical impedance spectroscopic techniques) revealed that the SWCNT and SWCNT-CoTAPc(mix) films showed comparable electrocatalytic responses towards the detection of DEAET and DMAET whereas competitive electrochemical behaviour was seen between SWCNT and SWCNT-NiTAPc modified BPPGEs. Using the BPPGE-SWCNT-CoTAPc(mix), the estimated catalytic rate constants (k) and diffusion coefficients (D) were higher for DEAET than for the DMAET. Also, the detection limits of approximately 8.0 and 3.0µM for DMAET and DEAET were obtained with sensitivities of 5.0×10−2 and 6.0×10−2 AM−1 for DMAET and DEAET, respectively. Unlike BPPGE-SWCNT-CoTAPc(mix) that detected the two sulfhydryls at slightly different potentials, BPPGE-SWCNT did not. The BPPGE-Ni gave enhanced Faradaic response for the redox probe ([Fe(CN)6]3−/4−) and also displayed enhanced electrocatalytic behaviour towards the detection of DMAET and DEAET with high sensitivity (~23x10−3 AM−1) and low detection limits (4.0 – 9.0 µM range). In comparison to other electrodes reported in the literature, BPPGE-Ni exhibits more promising features required for a simple, highly sensitive, fast and less expensive electrode for the detection of the hydrolysis products of V-type nerve agents in aqueous solution. The efficient response of the BPPGE-Ni is attributed to the high microscopic surface area of the nickel powder. The poor response of the BPPGE-Ni-SWCNT suggests that the nickel impurity in SWCNT did not show any detectable impact on the heterogeneous electron transfer kinetics of SWCNT. Unlike the nickel powder, SWCNT and CoTAPc-SWCNT, the NiTAPc-SWCNT hybrid did not show significant electrocatalysis towards the detection of the sulfhydryls. It is interesting, however, to observe for the first time that SWCNT induced crystallinity on the electropolymer of NiTAPc, and that such electropolymer exhibit charge-storage /-transfer properties that greatly enhance the electrochemical response of nitric oxide. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted
3

ADVANCED THERMAL MANAGEMENT FOR A SWITCHED RELUCTANCE MACHINE / THERMAL MANAGEMENT FOR A SWITCHED RELUCTANCE MACHINE

Marlow, Richard January 2016 (has links)
The thermal management of electric machines is investigated with the application of techniques to a Switched Reluctance Machine and a high-speed Switched Reluctance Machine. Two novel concepts for said management of a Switched Reluctance Machine are proposed and developed: Inter-Laminate Cooling and a Continuous Toroidal Winding. The Inter-Laminate Cooling concept is developed with application to an iron core inductor which serves as a proxy for the electric machine. The experimental results confirmed the capability of the method, expressed by the effectiveness, which defines the performance measure of the applied cooling method; a concept which itself is equally applicable to other cooling methods that may be applied to any electric machine. The effectiveness also describes the gain in allowable input power to the machine which is realized to reach the same thermal limit versus the case without Inter-Laminate Cooling. The Inter-Laminate Cooling was not applied in experimental test to a Switched Reluctance Machine due to the present economic and fabrication limitations. The Continuous Toroidal Winding concept, originally conceived to permit the consideration of a fluid capillary core type of winding to enhance machine cooling, is developed to allow for peripheral cooling of the machine windings and end windings. The Continuous Toroidal Winding version of the Switched Reluctance Machine is investigated for both its thermal and electrical performance in the context of a machine that is equivalent electromagnetically to its conventional counterpart. The Continuous Toroidal Winding Switched Reluctance Machine was found to perform thermally as tested, in a manner superior to that of the conventional machine where the Toroidal machine was simulated and researched at an equivalent level of operation to the conventional machine. The electrical performance of the Toroidal Switched Reluctance Machine although supportive of the simulation analysis used to develop the machine, was not fully conclusive. This may have been due to problematic iron cores used in the construction of the experimental machines. The application of the Inter-Laminate Cooling method to a Switched Reluctance Machine is considered on an analytical basis for the special case of a High Speed Switched Reluctance Machine and found to be of net positive benefit as the machine’s iron losses are dominant over its copper losses. Application of the Inter-Laminate Cooling method to a lower speed machine, whilst beneficial, is not sufficient to significantly impact the temperature of the machine’s windings such that it would offset the loss of specific torque and power. As such, Inter-Laminate Cooling is only applicable where the net benefit is positive overall; in that the gain in input power realized is sufficient to overcome the loss of specific power and torque which will occur due to the increased machine volume. The “effectiveness” and “gain” approach for the evaluation of cooling methods applied to electric machines is a concept which should be adopted to aid in the comparative understanding of the performance of myriad different cooling methods being applied to electric machines both in research and practice, of which there is only minimal understanding. / Thesis / Doctor of Philosophy (PhD)
4

Josephson-coupled superconducting regions embedded at the interfaces of highly oriented pyrolytic graphite

Ballestar, Ana, Barzola-Quiquia, José, Scheike, Thomas, Esquinazi, Pablo 02 August 2022 (has links)
Transport properties of a few hundreds of nanometers thick (in the graphene plane direction) lamellae of highly oriented pyrolytic graphite (HOPG) have been investigated. Current–voltage characteristics as well as the temperature dependence of the voltage at different fixed input currents provide evidence for Josephson-coupled superconducting regions embedded in the internal two-dimensional interfaces of HOPG, reaching zero resistance at low enough temperatures.
5

DETERMINAÇÃO DE HIDRAZINA POR VOLTAMETRIA DE ONDA QUADRADA SOBRE ELETRODO DE GRAFITE MODIFICADO COM FeTPyPz / HYDRAZINE DETERMINATION FOR VOLTAMMETRIC OF SQUARE SHAPED WAVE ON GRAPHITE ELECTRODE MODIFIED WITH FeTPyPz

Dantas, Luiza Maria Ferreira 22 August 2007 (has links)
Made available in DSpace on 2016-08-19T12:56:30Z (GMT). No. of bitstreams: 1 Luiza Maria Ferreira Dantas.pdf: 554629 bytes, checksum: e52ab366e6eca5730a202673574f26b5 (MD5) Previous issue date: 2007-08-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work, the determination of hydrazine (N2H4) in aqueous solutions was investigated by voltammetric techniques on pyrolytic graphite electrodes (GP) before and after modification with iron tetra-pyridinoporphyrazine (FeTPyPz). The modified electrode GP/FeTPyPz presented higher oxidation currents and better voltammetric profiles in comparison with the unmodified electrodes. This modified electrode exhibited two reversible peaks attributed to the redox processes: Fe(I)TPyPz/Fe(II)TPyPz and Fe(II)TPyPz/Fe(III)TPyPz. The pH optimization conditions were performed in solutions prepared by the mixture of different proportions of 0.1 mol L-1 sodium hydroxide (NaOH) and 0.1 mol L-1 phosphate buffer solutions in order to obtain solutions with pH varying from 7 to 13. In order to increase the sensitivity for hydrazine oxidation, three voltammetric techniques were tested: cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). The best results were provided by the latter one and the optimized conditions for hydrazine determinations were: i) electrolyte: 0,1 mol L-1 NaOH solution; ii) frequency: 30 s-1; pulse amplitude: 50 mV and scan increment: 8 mV. Under such conditions, the modified electrodes provided linear responses ranging from 5 up to 111 μmol L-1, with detection and quantification limits of 0.82 μmol L-1 and 2.7 μmol L-1, respectively. The investigated sensor presented relative standard deviation values for repeatability and reproducibility lower from 5%. The sensor was applied to analyze boiler water samples and a recovery average of 116 % was found. / Neste trabalho, a determinação de hidrazina (N2H4) em solução aquosa foi investigada com o uso de técnicas voltamétricas sobre eletrodos de grafite pirolítico (GP), antes e após a modificação com tetrapiridinoporfirazina de ferro (FeTPyPz). O eletrodo modificado GP/FeTPyPz apresentou correntes de oxidação da N2H4 mais acentuadas e com melhor perfil voltamétrico em relação ao eletrodo não modificado. Este eletrodo modificado apresentou dois picos reversíveis atribuídos aos processos redox: Fe(I)TPyPz/Fe(II)TPyPz e Fe(II)TPyPz/Fe(III)TPyPz. As condições de otimização do pH foram realizados em soluções preparadas através da mistura de diferentes proporções de solução de hidróxido de sódio (NaOH) 0,1 mol Lfi1 e tampão fosfato (KH2PO4) 0,1 mol Lfi1, a fim de obter soluções com pH variando de 7 a 13. Com o objetivo de aumentar a sensibilidade para a oxidação de hidrazina, testou-se três técnicas voltamétricas: voltametria cíclica (CV), voltametria de pulso diferencial (DPV), e voltametria de onda quadrada (SWV). Os melhores resultados foram obtitos através da técnica SWV e as condições otimizadas para a determinação de hidrazina foram: i) eletrólito: solução NaOH 0,1 mol Lfi1, ii) frequência de 30 sfi1, amplitude de pulso de 40 mV e incremento de varredura de 8 mV. Sob tais circunstâncias, o eletrodo modificado forneceu uma resposta linear entre 5 e 111 fimol Lfi1, com limite de detecção e quantificação de 0,82 fimol Lfi1 e 2,7 fimol Lfi1, respectivamente. O sensor investigado apresentou valores de desvio padrão relativo para estudos de repetibilidade da amostra e do sensor abaixo de 5%. O sensor foi aplicado em amostras de águas de caldeira e apresentou média de recuperação de 116%.
6

DETERMINAÇÃO DO HERBICIDA PARAQUAT SOBRE ELETRODOS DE GRAFITE PIROLÍTICO MODIFICADOS COM FTALOCIANINA DE COBALTO UTILIZANDO VOLTAMETRIA DE ONDA QUADRADA / DETERMINATION OF HERBICIDE PARAQUAT ON ELECTRODES OF PYROLYTIC GRAPHITE MODIFIED WITH COBALT PHTALOCYANINE USING WAVE SQUARE VOLTAMMETRY

Lopes, Ilanna Campelo 24 July 2006 (has links)
Made available in DSpace on 2016-08-19T12:56:38Z (GMT). No. of bitstreams: 1 Ilanna Campelo Lopes.pdf: 782855 bytes, checksum: 0cbaabd79c9d12083e00badf326ac1d0 (MD5) Previous issue date: 2006-07-24 / Determination of paraquat (PQ) in watery solutions was investigated with the technique of wave square voltammetry on pyrolytic graphite electrodes (PG) before and after modifications with metal phtalocyanines. The electrode modified with cobalt phthalocyanine (CoPc) presented PQ reduction currents more accented and voltammetrics profiles better with respect to the electrodes unmodified and modified with nickel phthalocyanine (NiPc), iron (FePc), manganese (MnPc) and in the acid form (H2Pc). This sensor presented two reversible peaks for the reduction of PQ next to - 0,71 V (peak 1) and - 1,10 V (peak 2) versus S C E. After optimization of cobalt phthalocyanine concentration and the adsorption time on electrode, the best analysis conditions for the PQ in 0,10 mol L-1 Britton-Robinson buffer solution (pH 7,0) was established: frequency of 100 s-1, wave amplitude of 50 mV and scan increment of 2 mV. In these conditions, the modified electrode obtained a linear response range from 5,00 x 10-7 to 2.91 x 10-5 mol L-1 (128,59 to 748,36 x 101 μg L-1) with detection and quantification limits equals to 1,44 x 10-7 mol L-1 (37,03 μg L-1) and 4,79 x 10-7 mol L-1 (123,26 μg L-1)1, respectively. The studied sensor presented values below 5%, in terms of relative standard deviation, for repeatability (0,58% (± 0,27) for N = 10) and reproducibility (1,58% (± 0,74) for N = 5) studies. The sensor was applied in natural water samples and the gotten results was presented recovery averages of 93,14% (± 7,16) and 119,25% (± 5,68) in two water samples analyzed. / A determinação de paraquat (PQ) em soluções aquosas foi investigada com a técnica de voltametria de onda quadrada sobre eletrodos de grafite pirolítico (GP) antes e após modificações com metaloftalocianinas. O eletrodo modificado com ftalocianina de cobalto (CoPc) apresentou correntes de redução do PQ mais acentuadas e melhores perfis voltamétricos em relação ao eletrodo não modificado e modificados com ftalocianina de níquel (NiPc), de ferro (FePc), de manganês (MnPc), e na forma ácida (H2Pc). Este sensor apresentou dois picos reversíveis para redução do PQ em torno de - 0,71 V (pico 1) e - 1,10 V (pico 2) vs E C S. Após otimizações da concentração da ftalocianina de cobalto e do tempo de adsorção no eletrodo, as melhores condições de análise para o PQ em solução tampão Britton- Robinson 0,10 mol L-1 (pH 7,0) estabelecidas foram: freqüência de 100 s-1, amplitude de pulsos de 50 mV e incremento de varredura de 2 mV. Nestas condições, o eletrodo modificado obteve uma resposta linear de 5,00 x 10-7 a 2,91 x 10-5 mol L-1 (128,59 a 748,36 x 101 μg L-1) com limites de detecção e quantificação iguais a 1,44 x 10-7 mol L-1 (37,03 μg L-1) e 4,79 x 10-7 mol L-1 (123,26 μg L-1), respectivamente. O sensor estudado apresentou valores abaixo de 5%, em termos de desvio padrão relativo, para estudos de repetibilidade (0,58% (± 0,27) para N = 10) e reprodutibilidade (1,58% (± 0,74) para N = 5). O sensor foi aplicado em amostras de águas naturais e os resultados obtidos apresentaram médias de recuperação de 93,14% (± 7,16) e 119,25% (± 5,68) em duas amostras de água analisadas.
7

Charakterizace elektrody modifikované pyridinoporfyrazinátovým filmem a její využití v elektrochemickém senzoru / Characterization of electrode modified by pyridineporphyrazinate film and its utilization in electrochemical sensor

Klusáčková, Monika January 2011 (has links)
In the diploma thesis the charge transfer reaction on thin layer N,N',N'',N'''-tetramethyl-tetra-3,4-pyridinoporphyrazinocobalt mediator is studied. The mediator is deposited on electrode surface formed by basal plane of highly ordered pyrolytic graphite. The modified electrode, which displays electrocatalytic activity to oxidation of propylene, has been characterized by cyclic voltammetry, backscattering spectroscopy and atomic force microscopy.
8

Protons and X-ray damaging effects on DNA self-assembled on Mylar foils and in solution in absence and in the presence of gold nanoparticles / Effets d'endomagement de Photons et rayons X sur l'ADN auto-assemblés sur de la feuille de Mylar et en solution en l'absence et en présence de nanoparticules

Khalil, Talat tariq 18 March 2016 (has links)
Cette thèse vise à étudier les nanoparticules d'or (NPOs) comme radio sensibilisateur et nano catalyseur afin d'améliorer la production d'espèces réactives de l'oxygène (EROS) et à fournir un aperçu de l'effet protecteur potentiel des acides aminés de base contre les effets des rayonnements ionisants afin d'étudier le mécanisme de dommages de l'ADN. En outre, il vise à améliorer notre connaissance des effets directs et indirects sur l'ADN plasmatique qui est une cible importante et sensible lors de l'étude des effets des rayonnements ionisants. Cette étude nécessite à la fois Ia bonne distribution et le contrôle de l'ADN déposé sur graphite HOPG. Nous avons procédé à la préparation de films (couches nanométriques à l’échelle) faite d'un complexe d'ADN avec des amines, ainsi que les acides aminés basiques. Nous avons caractérisé le déposé sec par microscopie a force atomique et par XPS. Nous avons montré que les couches contenant des acides aminés basiques sont très denses et que la protection contre les dommages de l'ADN après re-dissolution dans l'eau est très efficace. Ensuite, nous avons déposé l'ADN plasmatique à sec soul sur des feuilles minces de mylar et d'exposé ces films à un faisceau de protons à différentes énergies, Nous avons montré que, dans le value de pic de Bragg d'énergie a protons énergies inferieure a 500 keV il y a un rendement Cleve de protons a endommagé l'ADN. L'effet indirect a donc été étudié en exposant l'ADN plasmatique en solution aqueuse par rayons X ultra-mous. Nous avons procédé a de telles expériences en utilisant 100 lit de solution d'ADN plasmatique avec et sans différentes concentrations de 2-amino-2-hydroxymethyl-propane-1,3-diol, (Tris) et l'arginine (Arg) à température ambiante et sous agitation. Une très bonne procédure expérimentale. Nous avons montré que les rendements pour les pauses ADN simples brins ont permis au ratio indirect des effets directs à déterminer à 96% en bon accord avec la valeur de 97% découlant d’une étude basée sur l’irradiation aux rayons gamma de solutions congelées de l’ADN plasmatique. Nous analysons nos résultats et nous suggérons que les produits secondaires de Arginine réagissent avec les radicaux OH pour produire des effets secondaires; notamment en raison du fait que, contrairement au Tris, Arg est capable de liaison à l'ADN à l'extérieur et également à l'intérieur de la double hélice. Nous avons exposé également l'ADN de plasmide en solution aqueuse et complexe aux deux autres acides aminés basiques (lysine et histidine) par rayons X ultra-mous. Nous avons constaté que la présence de ces acides aminés augmente également la détérioration de l'ADN et suggère que les acides aminés sont donc également susceptibles de produire des effets secondaires. Enfin, nous avons étudié Ie rôle de nanoparticules d'or (NPO) dans le renforcement de la sensibilisation de la radio de l'ADN. En utilisant de nouveaux protocoles expérimentaux, nous avons fini à interpréter l'interaction du (NPOs) avec ionisation rayonnement dans des solutions aqueuses oxygénées. Pour obtenir une meilleure compréhension des mécanismes de sensibilisation de radio par NPOs, nous avons utilisé une variété de espèces détritivores, spécifiques et réactives d'oxygène et l'ADN plasmatique comme sonde afin de favoriser les voies donnees et de determiner laquelle d'entre elles est la plus efficace dans l'ADN dommageable. Cette étude a démontré pour la première fois que les NPOs contribuent en permanence à l'amélioration de la production de OH en utilisant un stock potentiel maintenu sous la forme d'HO2 • / 02 • - et H202 produits de radiolyse de l'eau primaire. Nous avons montre en effet que H202 peut réagir avec NPOs pour produire • OH radicaux. / This thesis aims at studying the gold nanoparticles (GNPs) as radiosensitizer and nanocatalyst in order to enhance the generation of reactive oxygen species (ROSs) and at providing insight into the potential protective effect of basic amino acids against ionizing radiation effects in order to study the mechanism of DNA damage. Also, it aims at improving our knowledge of direct and indirect effect on plasmid DNA which is an important and sensible target when studying ionizing radiation effects. This study required both the good distribution and control of the DNA deposited on HOPG (Highly Ordered Pyrolytic Graphite). We carried out the preparation of films (nanometer scaled layers) made of complex of DNA with diamines as wel as basic amino acids. We have characterized dry deposited by AFM (Atomic Force Microscopy) and by XPS (X-ray photoelectron spectroscopy). We have shown that the layers containing basic amino acids are very dense and that the protection against DNA damage after re-dissolution in water is very effective. Then, we have deposited dry plasmid DNA alone on thin mylar foils and exposed those films to a proton beam at various energies. We have shown that in the Bragg-peak energy range i.e. at proton energies lower than 500 keV there is a high efficiency of protons to damage DNA. The indirec effect was thus studied by exposing plasmid DNA in aqueous solution by (USX). We carried out such experiments by using 100 pit of plasmid DNA solution with and without different concentrations of 2-Amino-2-hydroxymethyl-propane-1,3-diol (Tris) and arginine (Arg) at ambient temperature and under stirring. A very good agreement was found with the rare data dealing with DNA plasmid exposed to Al Ka photons at low temperature (T < 277 K), which therefore validated the experimental procedure. We showed that the yields for DNA single strand breaks determined enabled the ratio of indirect to direct effects to be determined at 96.2%; in good agreement with the value of 97.7% stemming from a study based on y-ray irradiation of frozen solutions of plasmid DNA. We analyze our results and suggest that secondary products of Arginine react with OH radicals to produce side effects; notably due to the fact that contrary to Tris, Arg is capable of binding DNA outside but also inside the double-helix. We exposed also the plasmid DNA in aqueous solution and complexed to the two other basic amino acids (histidine and lysine) by USX. We found that the presence of tilos amino acids also increases DNA damage and suggest that those amino acids are therefore also prone to produce side effects. Lastly, we studied the role of Gold Nano Particles (GNPs) in enhancing DNA radio sensitization. By using new experimental protocols, we achieved to interpret the interaction of GNPs with ionization radiation in oxygenated aqueous solutions. To get better insight into the mechanisms of radiosensitization by GNPs, we used a variety of specific reactive oxygen species scavengers and plasmid DNA as a probe in order to favor given pathways and to determine which of them is the most effective in damaging DNA. This study has demonstrated for the first time that the GNPs contribute permanently to the enhancement of ■OH production by using a potential stock kept under the form of 1102•/02•- and H202 primary water radiolysis products. We showed indeed that H202 ca react with GNPs to produce •0H radicals.
9

Charakterizace a analytické využití pyridinoporfyrazinátu kobaltu jako neplatinového mediátoru v elektrokatalýze vodíku / Characterization and Analytical Application of Cobalt Pyridinoporfyrazinate as a Non-Platinum Mediator in Hydrogen Electrocatalysis

Klusáčková, Monika January 2019 (has links)
This work reports on the cobalt pyridinoporphyrazinate (CoTmtppa) as a platinum-group metal-free catalyst for hydrogen evolution and oxidation reactions with the possibility of use in hydrogen energy and hydrogen potentiometric sensing. A different interaction of CoTmtppa with various electrode substrates, highly oriented pyrolytic graphite (HOPG) and annealed gold (Au(111)), affects its electrocatalytic behaviour in hydrogen reactions. The formation of a hydride-type complex with the bonding of hydrogen atoms to cobalt centre is supposed to be the rate-determining step. In the case of hydrogen evolution, the maximum catalytic activity of mediator was reached at pH = 11,0, when the HOPG/CoTmtppa showed overpotential decrease by 300 mV and an almost 60-fold increase of current densities compared to HOPG. The electrocatalytic activity of Au(111)/CoTmtppa resulted in a further decrease of overpotential by 175 mV in comparison with HOPG/Co(I)Tmtppa. The electrochemical oxidation of hydrogen was found to depend on hydrogen source which was electrochemically generated on-site or molecular hydrogen supplied from an external source. In the case of electrochemically generated hydrogen, the maximum activity of HOPG/CoTmtppa was reached at pH = 2.1 and an additional it was observed 50 % increase in current...
10

Studium redoxních reakcí a adsorpce 4-nitrofenyltriazolem značených nukleosidů a kresolů na borem dopovaných diamantových elektrodách pro vývoj elektroanalytických metod / Study of redox reactions and adsorption of 4-nitrophenyl triazole labeled nucleosides and cresols on boron doped diamond electrodes for development of electroanalytical methods

Vosáhlová, Jana January 2020 (has links)
In this work, the application of boron-doped diamond electrodes with various surface pre- treatment were tested on selected oxidizable and reducible model compounds, specifically para and ortho cresols and 2'-deoxycytidine and 7-deazaadenosine labeled by 4-nitrophenyl triazole. The aim of the study was the investigation of electrochemical and adsorptive processes with respect to the development of electroanalytical methods of detection of the selected compounds, or utilization of boron-doped diamond electrodes as detectors in liquid-flow systems. Cresols were used as the model oxidizable compound. On O-terminated and polished boron- doped diamond electrodes, cresols provide oxidation signal owing to their oxidation to methylphenoxy radical at comparable potentials as on other carbon-based electrodes used as a reference in this work, i.e., glassy carbon electrode, pyrolytic graphite electrode, and carbon paste electrode. These carbon electrode materials show relatively high propensity to adsorption of reaction products, while such adsorption is minimal on boron-doped diamond. In situ anodic activation allows for a rapid regeneration of boron-doped diamond surface prior to each scan. A differential pulse voltammetric method that was developed with a detection limit of 0.61 mol∙l-1 to 2.97 mol∙l-1...

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