Submitted by Marilene Donadel (marilene.donadel@unioeste.br) on 2018-04-25T00:28:56Z No. of bitstreams: 1 Joelmir_Santos_2016.pdf: 3759768 bytes, checksum: 953ccb765b5bea358bd87b6b493ab5cb (MD5) / Made available in DSpace on 2018-04-25T00:28:56Z (GMT). No. of bitstreams: 1 Joelmir_Santos_2016.pdf: 3759768 bytes, checksum: 953ccb765b5bea358bd87b6b493ab5cb (MD5) Previous issue date: 2016-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This study aimed the evaluation and application of methodology for multielement analyses by total reflection X-ray fluorescence spectrometry (TXRF) in order to provide analyte concentration measurements with accuracy and precision. Using the energy and intensity of the spectral lines of characteristic X-ray, a series of chemicals were identified and quantified, respectively, with a concentration below part per million to a few parts per billion, especially for transition metals. To ensure statistical reliability and reproducibility, a methodology based on the deposition of fine particles, less than 50 m, representative sample and uniformly spread on a quartz flat reflector, which was extremely clean and positioned at the angular condition of maximum reflectivity of monochromatic X-rays was applied. To ensure uniformity on the support surface and the sample representativeness, a number of replicas of specific quantities of samples, in the form of a fine powder was added in a diluted viscous organic solution containing a well-known concentration of an element choosing as internal standard. An aliquot of the viscous solution containing both the suspended particulate sample and an internal standard was deposited at the center of the quartz reflector and dried, yielding a very thin layer of particulates. First, the instrumental TXRF was previously evaluated for its operation, spectral response and recovery of transition metal concentrations in a test sample supplied by the manufacturer. The reproducibility of the elemental concentration measurements was tested with a combination of the number of experimental replicates (five) and analytical (three) for each type of environmental matrix samples, namely certified reference materials or CRMs. Six types of CRMs were tested: river sediment, tomato leaves, rice, fish muscle, bone and bovine liver. The data were statistically processed data, resulting in a series of average and uncertainty values of the analyte concentrations was compared to certified reference values, reported in the technical reports of CRM. Regarding the multielement character of the TXRF technique, there was a good recovery, about 100%, for most of the certified concentrations of the referenced analytes in the six CRMs within the margin of variability of results found by both the TXRF technique and reports. It was also found that the detection limit depends on the density matrix of the material under study. However, the transition elements were those with the lowest values of detection limits. Having a good recovery of majority analyte concentrations in Buffalo River sediment reference material, the same methodology was applied to sediment material analysis of Bezerra stream that was collected in three locations and for a period of three years. A number of chemicals has been identified through their spectral lines K and L and quantified following the internal standard method. The set of concentration data was statistically processed from the point of view of the normality of the data and an analysis of principal components, revealing a systematic presence of high concentrations of heavy metals such as lead and chromium, comparatively higher those recommended by current environmental legislation (CONAMA 420/2009) as the maximum permissible limits. / Este trabalho teve como objetivo a avaliação e aplicação de metodologia para análise multielementar por meio da espectrometria de fluorescência de raios X por reflexão total (TXRF), a fim de fornecer medidas de concentração de analitos com acurácia e precisão. Usando a energia e a intensidade das linhas espectrais de raios X característicos, uma série de elementos químicos foram identificados e quantificados, respectivamente, com concentração abaixo de parte por milhão até poucas partes por bilhão, principalmente para metais de transição. A fim de garantir a confiabilidade e reprodutibilidade estatística, foi aplicada uma metodologia que se baseia na deposição de particulados finos, menores que 50 m, representativos da amostra e uniformemente distribuídos sobre um refletor plano de quartzo, previamente limpo, na condição angular de máxima refletividade de raios X monocromáticos. Para garantir a uniformidade no suporte e a representatividade da amostra, uma série de réplicas de quantidades específicas de amostras, na forma de um pó fino, foi adicionada em solução orgânica viscosa diluída contendo uma concentração conhecida de um elemento na qualidade de padrão interno. Uma alíquota da solução viscosa contendo ambos o particulado de amostra em suspensão e o padrão interno foi depositada no centro do refletor de quartzo e seca, obtendo-se uma camada fina de particulado. Primeiramente, o instrumental TXRF foi previamente avaliado quanto a operação, resposta espectral e recuperação de concentrações de metais de transição de uma amostra de teste fornecido pelo fabricante. A reprodutibilidade das medidas de concentração elementar foi testada com uma combinação da série de réplicas experimentais (cinco) e analíticas (três) para cada tipo de matriz de amostras ambientais, chamadas de Materiais de Referência Certificados ou MRC. Foram testados seis tipos de MCRs: sedimento de rio, folhas de tomate, arroz, músculo de peixe, osso e fígado bovino. Foram processados estatisticamente a série de dados de concentrações elementares de cada MCR, obtendo-se o valor médio e incerteza da concentração de cada analito de referência o qual foi comparado ao reportado nos laudos técnicos dos MCR. Considerando o caráter multielementar da técnica TXRF, verificou-se uma boa recuperação, em torno de 100%, da maioria das concentrações referenciadas e certificadas dos analitos nos seis MCRs, dentro da margem de variabilidade dos resultados encontrados pela técnica TXRF e reportados pelos laudos. Verificou-se também que o limite de detecção depende da densidade da matriz do material sob estudo. Contudo, os elementos de transição foram os que apresentaram os menores valores de limites de detecção. Tendo a boa recuperação das concentrações de analitos maioritários no material de referência sedimento Buffalo River, foi aplicada a mesma metodologia para análise de material de sedimento do córrego Bezerra-Cascavel que foi coletado em três locais ao longo dele e por um período de três anos. Uma série de elementos químicos foram identificados através de suas linhas espectrais K e L, e quantificados seguindo o método do padrão interno. O conjunto de dados de concentração foi processado estatisticamente do ponto de vista da normalidade dos dados e feita uma análise de componentes principais, revelando uma sistemática presença de altas concentrações de metais pesados, tais como chumbo e cromo, comparativamente maiores daqueles preconizados pela atual legislação ambiental (CONAMA 420/2009) quanto aos limites máximos permissíveis.

The purpose of this study was to investigate physics undergraduate students’ conceptual change in the concepts of electric potential and energy (EPE) and electromagnetic induction (EMI). Along with this, categorization of students’ conceptions was done based on students’ epistemological and ontological descriptions of these concepts. In addition, the effect of cognitive perturbation using physics interactive simulations (CPS) in relation to cognitive conflict using physics interactive simulations (CCS) was investigated. A pragmatic mixed methods approach was used in a quasi-experimental design. Data were collected by using the modified Diagnostic Exam of Electricity and Magnetism (DEEM), focus group discussions (FGD) and concept maps (CM). Framework analysis was conducted separately on FGD and CM qualitative data to categorize students’ conceptions while concentration analysis was used to categorize students’ responses to the modified DEEM into three levels, during pre and post intervention. In the qualitative results, six categories of alternative conceptions (naive physics, lateral alternative conceptions, ontological alternative conceptions, Ohm’s P-Primes/ P-Primes, mixed conceptions and loose ideas) and two categories of conceptual knowledge (hierarchical and relational) were identified. The alternative conceptions were less frequently and inconsistently revealed within and across the categories. It was concluded that the categories have common characteristics of diversified distribution of alternative conceptions and multiple alternative conceptions of specific concepts within and across the categories. Most of the categories found in pre intervention persisted in post intervention, but with a lesser percentage extensiveness of categories of alternative conceptions in the CPS than in the CCS class and more percentage extensiveness of categories of conceptual knowledge in the CPS than in the CCS class. ANCOVA was separately conducted on the scores of 45 students on the modified DEEM and CM tests to compare the effectiveness of the CCS and CPS. The results showed a significant difference between the two classes of the post test scores on the DEEM test, (1, 36) = 4.66, p=0.04 and similarly, on the CM test, (1, 31) = 8.33, p=0.007. Consequently, it was concluded that there is a statistically significant difference between CPS and CCS in changing students’ alternative conceptions towards scientific conceptions favoring CPS. To characterize and compare students’ conceptual change of both treatment classes, Hake’s average normalized gain <g> from pre to post scores (the modified DEEM and the CM) were analyzed. Finally, it is suggested that in abstract conceptual areas of EM, cognitive perturbation through interactive simulations is more effective than cognitive conflict through interactive simulations in facilitating conceptual change, and, thus, should guide classroom instruction in the area. Furthermore, recommendations are also suggested for guiding future research in this area. / Science and Technology Education / D. Phil. (Mathematics, Science and Technology Education (Physics Education))

The purpose of this study was to investigate physics undergraduate students’ conceptual change in the concepts of electric potential and energy (EPE) and electromagnetic induction (EMI). Along with this, categorization of students’ conceptions was done based on students’ epistemological and ontological descriptions of these concepts. In addition, the effect of cognitive perturbation using physics interactive simulations (CPS) in relation to cognitive conflict using physics interactive simulations (CCS) was investigated. A pragmatic mixed methods approach was used in a quasi-experimental design. Data were collected by using the modified Diagnostic Exam of Electricity and Magnetism (DEEM), focus group discussions (FGD) and concept maps (CM). Framework analysis was conducted separately on FGD and CM qualitative data to categorize students’ conceptions while concentration analysis was used to categorize students’ responses to the modified DEEM into three levels, during pre and post intervention. In the qualitative results, six categories of alternative conceptions (naive physics, lateral alternative conceptions, ontological alternative conceptions, Ohm’s P-Primes/ P-Primes, mixed conceptions and loose ideas) and two categories of conceptual knowledge (hierarchical and relational) were identified. The alternative conceptions were less frequently and inconsistently revealed within and across the categories. It was concluded that the categories have common characteristics of diversified distribution of alternative conceptions and multiple alternative conceptions of specific concepts within and across the categories. Most of the categories found in pre intervention persisted in post intervention, but with a lesser percentage extensiveness of categories of alternative conceptions in the CPS than in the CCS class and more percentage extensiveness of categories of conceptual knowledge in the CPS than in the CCS class. ANCOVA was separately conducted on the scores of 45 students on the modified DEEM and CM tests to compare the effectiveness of the CCS and CPS. The results showed a significant difference between the two classes of the post test scores on the DEEM test, (1, 36) = 4.66, p=0.04 and similarly, on the CM test, (1, 31) = 8.33, p=0.007. Consequently, it was concluded that there is a statistically significant difference between CPS and CCS in changing students’ alternative conceptions towards scientific conceptions favoring CPS. To characterize and compare students’ conceptual change of both treatment classes, Hake’s average normalized gain <g> from pre to post scores (the modified DEEM and the CM) were analyzed. Finally, it is suggested that in abstract conceptual areas of EM, cognitive perturbation through interactive simulations is more effective than cognitive conflict through interactive simulations in facilitating conceptual change, and, thus, should guide classroom instruction in the area. Furthermore, recommendations are also suggested for guiding future research in this area. / Science and Technology Education / D. Phil. (Mathematics, Science and Technology Education (Physics Education))