Técnicas de Mistura de 4 Ondas foram utilizadas para se estabelecer e observar redes de difração dinâmicas formadas pela população de íons Cr+3 e através disto estudamos os efeitos de saturação em Conjugação de Fase por Mistura Degenerada de 4 Ondas (CFMD40) em cristais de GdAlO3 : Cr+3 (Aluminato de Gadolínio dopado com Cr+3) e Al2O3 : Cr+3 (Rubi). Foi utilizado um laser de Argonio CW em &lambda = 514nm para investigar experimentalmente o comportamento estacionário e transiente da eficiência (ou refletividade) na CFMD40, onde obtivemos um bom acordo com os modelos teóricos utilizados. Pela primeira vez foi registrada a resposta temporal transiente do campo conjugado em CFMD40 para cristais de GdAlO3 : Cr+3, onde foi desenvolvida e utilizada uma nova técnica de medida. Nossos resultados de eficiência estacionaria para o cristal de GdAlO3 : Cr+3 são, segundo nosso conhecimento, os mais altos obtidos neste tipo de material utilizando-se lasers contínuos neste comprimento de onda. Realizamos também um experimento onde podemos comprovar a participação de ambas as redes absorptiva e dispersiva induzida nestes materiais fato este considerado em nosso modelo teórico. / Four Wave Mixing techniques were used to establish and probe dynamic gratings generated by Cr+3 ions population. By this method this we have studied the saturation effects in phase conjugation by Degenerate Four- wave Mixing (DFWM) in GdAlO3 : Cr+3 (Cr+3 doped Gadolineum Aluminatum) and Al2O3 : Cr+3 (Ruby). An Argon ion laser at &lambda = 514nm was used to investigate the stationary and transient behavior of efficiency in DFWM, where we have obtained good agreement with the theoretical models. For the first time the transient response of conjugated field by DFWM was measured in a GdAlO3 : Cr+3 crystal, using a new experimental technique. In the GdAlO3 : Cr+3 sample we obtained a maximum DFWM stationary efficiency of approximately 10%, which as far as we know, is the highest value achieved in this kind of material using a CW laser at this wavelength. We have also performed an experiment to probe the both contribution of absorptive and dispersive induced gratings in these materials, as we have considered in our theoretical model.

Técnicas de Mistura de 4 Ondas foram utilizadas para se estabelecer e observar redes de difração dinâmicas formadas pela população de íons Cr+3 e através disto estudamos os efeitos de saturação em Conjugação de Fase por Mistura Degenerada de 4 Ondas (CFMD40) em cristais de GdAlO3 : Cr+3 (Aluminato de Gadolínio dopado com Cr+3) e Al2O3 : Cr+3 (Rubi). Foi utilizado um laser de Argonio CW em &lambda = 514nm para investigar experimentalmente o comportamento estacionário e transiente da eficiência (ou refletividade) na CFMD40, onde obtivemos um bom acordo com os modelos teóricos utilizados. Pela primeira vez foi registrada a resposta temporal transiente do campo conjugado em CFMD40 para cristais de GdAlO3 : Cr+3, onde foi desenvolvida e utilizada uma nova técnica de medida. Nossos resultados de eficiência estacionaria para o cristal de GdAlO3 : Cr+3 são, segundo nosso conhecimento, os mais altos obtidos neste tipo de material utilizando-se lasers contínuos neste comprimento de onda. Realizamos também um experimento onde podemos comprovar a participação de ambas as redes absorptiva e dispersiva induzida nestes materiais fato este considerado em nosso modelo teórico. / Four Wave Mixing techniques were used to establish and probe dynamic gratings generated by Cr+3 ions population. By this method this we have studied the saturation effects in phase conjugation by Degenerate Four- wave Mixing (DFWM) in GdAlO3 : Cr+3 (Cr+3 doped Gadolineum Aluminatum) and Al2O3 : Cr+3 (Ruby). An Argon ion laser at &lambda = 514nm was used to investigate the stationary and transient behavior of efficiency in DFWM, where we have obtained good agreement with the theoretical models. For the first time the transient response of conjugated field by DFWM was measured in a GdAlO3 : Cr+3 crystal, using a new experimental technique. In the GdAlO3 : Cr+3 sample we obtained a maximum DFWM stationary efficiency of approximately 10%, which as far as we know, is the highest value achieved in this kind of material using a CW laser at this wavelength. We have also performed an experiment to probe the both contribution of absorptive and dispersive induced gratings in these materials, as we have considered in our theoretical model.

This master's thesis is focused on the determination of 6-thioguanine (6-T) by DC voltammetry (DCV), differential pulse voltammetry (DPV) and flow injection analysis with electrochemical detection (FIA-ED) on a boron doped diamond electrode (BDDFE). The optimum conditions for determination of 6-T were found and under these conditions, concentration dependences were measured and the limits of quantification (LOQ) were calculated for each method. Medium of 60% methanol and phosphate buffer (PB) pH 2,0 was chosen as optimum for DCV and DPV determination of 6-T at BDDFE. For both DCV and DPV, the linear concentration dependences were obtained in concentration ranges of 6-T from 2 µmol·l-1 to 10 µmol·l-1 with LOQ 0,9 µmol·l-1 for DCV and 1,5 µmol·l-1 for DPV. Lower LOQ was achieved in PB pH 2,0, where LOQ was 0,6 µmol·l-1 for both DCV and DPV, but the problem was lower repeatability. In PB pH 2 6-T was determined by DCV in drinking and river water with LOQ 1,3 µmol·l-1 in both drinking and river water. The possibility of solid phase extraction was investigated as a method for preliminary separation of 6-T from urine. For FIA under optimized conditions (polarization potential 1300 mV, flow rate 5 ml·min1 and sample volume 50 µl) the linear concentrations dependences were obtained in concentration ranges...