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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

Analysis of Faculty Evaluation by Students as a Reliable Measure of Faculty Teaching Performance

Twagirumukiza, Etienne 11 August 2011 (has links)
Most American universities and colleges require students to provide faculty evaluation at end of each academic term, as a way of measuring faculty teaching performance. Although some analysts think that this kind of evaluation does not necessarily provide a good measurement of teaching effectiveness, there is a growing agreement in the academic world about its reliability. This study attempts to find any strong statistical evidence supporting faculty evaluation by students as a measure of faculty teaching effectiveness. Emphasis will be on analyzing relationships between instructor ratings by students and corresponding students’ grades. Various statistical methods are applied to analyze a sample of real data and derive conclusions. Methods considered include multivariate statistical analysis, principal component analysis, Pearson's correlation coefficient, Spearman's and Kendall’s rank correlation coefficients, linear and logistic regression analysis.
2

Melhoria do processo Hatschek, por meio de tratamento de dados históricos, para fabricação de telhas onduladas. / Improving the process Hatschek, by means of treatment of historical data for manufacture of tiles wavy.

Oliveira, Aline Basso de 09 April 2010 (has links)
As telhas de cimento-amianto são utilizadas mundialmente nas construções comerciais, residenciais e industriais. O amianto foi a primeira aplicação de fibra natural em escala industrial. Esta fibra foi incorporada na forma do mineral (asbesto) como reforço de matrizes à base do cimento. O processo de fabricação de telhas de cimento-amianto mais utilizado mundialmente foi patenteado em 1900 por Ludwig Hatschek, recebendo o mesmo nome. O objetivo deste trabalho foi a melhoria do processo industrial (Hatschek) de fabricação de telha de cimento-amianto, com o uso de métodos estatísticos. Inicialmente as variáveis mais influentes no processo foram identificadas empregando-se o teste de correlação de Pearson e o Cp de Mallows que permitiu a escolha do melhor subconjunto da regressão (R², R²ajustado, Cp de Mallows e o desvio padrão do modelo). A seleção dessas variáveis permitiu a construção de modelos de regressão para o processo, para as respostas resistência mecânica e densidade da telha. Devido à análise de duas respostas, foi realizada uma otimização numérica por meio da função desejabilidade (desirability function), que é baseada na idéia de que a qualidade de um produto ou processo que tem múltiplas respostas depende de encontrar as variações do processo que atendem a todas as restrições impostas, sejam elas econômicas ou normas aplicáveis ao produto final. Com o resultado da otimização estabeleceram-se faixas de variação das variáveis mais influentes, que permitissem a operação do processo sob controle. Também, pode ser concluído que para a densidade de ambas as telhas (5 mm e 6 mm) encontraram-se modelos coerentes para serem usados mesmo após alguma modificação na máquina, enquanto que para a resistência os parâmetros dos modelos devem ser reajustados sempre que houver alguma modificação durante a parada da máquina. / Roofing tiles of the asbestos cement composites are used world-wide in the commercial, residential and industrial constructions. Asbestos was the first natural fiber application in industrial scale. This fiber was incorporated into the cimentitious matrices to overcome this weakness. The manufacturing process of asbestos-cement tiles most commonly used worldwide was patented in 1900 by Ludwig Hatschek, which gave his own name to this procedure. Considering that, this study aimed to improve the manufacturing process of roofing tiles of the asbestos cement composites, using several statistical methods. Firstly, the most influent variables were identified using the Pearson Correlation test and the Mallows Cp test, which provided the choice of the best subsets regression (R ², R ² adjusted, Mallows Cp and the standard deviation of this empirical model). The selection of these variables allowed the construction of regression models for the mechanical resistance and tile density responses. In order to fulfill the requirement of an appropriate analysis for two responses, a numerical optimization by means of desirability function was applied. This optimization is based on the premise that a product quality or process having multiple responses depends on finding all the variations that fulfill the imposed constraints. Even if these constraints were economic or norms applied to the final product. The optimization results established ranges of variation including the most influents variables, i.e., the ones that allow the process to run under control. Also, we conclude that for the density of both tiles (5 mm and 6 mm) were found consistent models to be used even after some eventual change in machine. For the resistance, however, the parameters of the models must be readjusted whenever it has some modification during the shutdown of the machine.
3

Melhoria do processo Hatschek, por meio de tratamento de dados históricos, para fabricação de telhas onduladas. / Improving the process Hatschek, by means of treatment of historical data for manufacture of tiles wavy.

Aline Basso de Oliveira 09 April 2010 (has links)
As telhas de cimento-amianto são utilizadas mundialmente nas construções comerciais, residenciais e industriais. O amianto foi a primeira aplicação de fibra natural em escala industrial. Esta fibra foi incorporada na forma do mineral (asbesto) como reforço de matrizes à base do cimento. O processo de fabricação de telhas de cimento-amianto mais utilizado mundialmente foi patenteado em 1900 por Ludwig Hatschek, recebendo o mesmo nome. O objetivo deste trabalho foi a melhoria do processo industrial (Hatschek) de fabricação de telha de cimento-amianto, com o uso de métodos estatísticos. Inicialmente as variáveis mais influentes no processo foram identificadas empregando-se o teste de correlação de Pearson e o Cp de Mallows que permitiu a escolha do melhor subconjunto da regressão (R², R²ajustado, Cp de Mallows e o desvio padrão do modelo). A seleção dessas variáveis permitiu a construção de modelos de regressão para o processo, para as respostas resistência mecânica e densidade da telha. Devido à análise de duas respostas, foi realizada uma otimização numérica por meio da função desejabilidade (desirability function), que é baseada na idéia de que a qualidade de um produto ou processo que tem múltiplas respostas depende de encontrar as variações do processo que atendem a todas as restrições impostas, sejam elas econômicas ou normas aplicáveis ao produto final. Com o resultado da otimização estabeleceram-se faixas de variação das variáveis mais influentes, que permitissem a operação do processo sob controle. Também, pode ser concluído que para a densidade de ambas as telhas (5 mm e 6 mm) encontraram-se modelos coerentes para serem usados mesmo após alguma modificação na máquina, enquanto que para a resistência os parâmetros dos modelos devem ser reajustados sempre que houver alguma modificação durante a parada da máquina. / Roofing tiles of the asbestos cement composites are used world-wide in the commercial, residential and industrial constructions. Asbestos was the first natural fiber application in industrial scale. This fiber was incorporated into the cimentitious matrices to overcome this weakness. The manufacturing process of asbestos-cement tiles most commonly used worldwide was patented in 1900 by Ludwig Hatschek, which gave his own name to this procedure. Considering that, this study aimed to improve the manufacturing process of roofing tiles of the asbestos cement composites, using several statistical methods. Firstly, the most influent variables were identified using the Pearson Correlation test and the Mallows Cp test, which provided the choice of the best subsets regression (R ², R ² adjusted, Mallows Cp and the standard deviation of this empirical model). The selection of these variables allowed the construction of regression models for the mechanical resistance and tile density responses. In order to fulfill the requirement of an appropriate analysis for two responses, a numerical optimization by means of desirability function was applied. This optimization is based on the premise that a product quality or process having multiple responses depends on finding all the variations that fulfill the imposed constraints. Even if these constraints were economic or norms applied to the final product. The optimization results established ranges of variation including the most influents variables, i.e., the ones that allow the process to run under control. Also, we conclude that for the density of both tiles (5 mm and 6 mm) were found consistent models to be used even after some eventual change in machine. For the resistance, however, the parameters of the models must be readjusted whenever it has some modification during the shutdown of the machine.
4

Evaluation of breeding practices and morphological characterisation of donkeys in three selected villages of the Blouberg Local Municipality, in the Limpopo Province, South Africa

Maswana, Masixole January 2022 (has links)
Thesis(M.Sc. (Animal Production)) -- University of Limpopo, 2022 / Donkeys continue to play a significant role in draught power activities for both rural and urban regions in underdeveloped countries, where they are commonly employed for transportation of goods and movement of people at extremely low prices. The study sought to determine donkey farmers' breeding practices as well as donkey morphological characterization in three villages such as Thorp, Archibalt and Genau of the Blouberg Local Municipality. A total of 21 donkey farmers and 74 donkeys were used to collect data. The following Morphological traits characterized were; Head length (HL), Ear length (EL), Neck length (NL), Chest width (CW), Back length (Bal), Body length (BoL), Hips width (HW), Umbilical circumference (UC), Back height (BH), Height at the rump (HR), Thoracic circumference (TC), Chest depth (CD), Withers Height (WH), Front leg length (FLL), Cannon circumference (CC), Cannon length (CL), Cannon height (CH) and Body weight (BW). Descriptive statistics, Chi-square tests, Analysis of variance (ANOVA), Pearson correlation, and Rank Index were used for data analysis. Education level of the farmers in the three villages was significantly different (p<0.05) with the majority of farmers having secondary education. There was no significant difference (p>0.05) amongst the villages on different reasons behind keeping donkeys. The results showed a significant difference (p<0.05) in inbreeding knowledge by the farmers amongst the three villages. The selection criteria used across the three villages were not significantly different (p>0.05). Rank and Indices in selection of male donkeys looked at body size (0.39), growth rate (0.19), Draught power performance (0.14), and for overall preference in female donkeys it was body size (0.26), twinning ability (0.23) and mothering ability (0.15). Body size and growth rate where the most important traits to donkey farmers. The coat colours were not significantly different (p>0.05). In all the eighteen measured traits, only four (BaL, HW, BH and FLL) showed a significant difference (p<0.05) among the three villages. BW in male donkeys was not significantly correlated (p>0.05) with HL, EL, NL, BaL, HW, FLL, CC, CH, CL but was positively correlated (p<0.05) with BoL (r = 0.34), UC (r = 0.35), TC (r = 0.33), CD (r = 0.31), CW (0.94), BH (r = 0.41), HR (0.60), and WH (r = 0.58). BW in female donkeys was not significantly correlated (p>0.05) with NL, BaL, TC, and CL but positively significant correlated (p<0.05) with HL, EL, BoL, HW, UC, FLL and CC CW, BH, HR, WH and CH with correlation coefficient values ranging from 0.34 to 0.75. The farmers had no breeding program in place the donkeys were allowed to mate on their own without designed breeding program. Selection of donkeys to be part of the heard was based on physical attributes, such length It was concluded that donkey farmers in Genau, Archibalt, and Thorp villages engaged in breeding practices that could be valuable in construction of a community-based breeding program.
5

Porovnání výsledků zátěžových testů na kajakářském ergometru s dosahovaným výkonem v rychlostní kanoistice / Comparison of performance tests results determined during kayak spiroergometry with achieved kayak paddling performance

Štěrba, Jan January 2013 (has links)
- 6 - Abstract Title: Comparison of performance tests results determined during kayak spiroergometry with achieved kayak paddling performance. Objectives: The aim of the study was to determine relationships between functional parameters values found during kayak spiroergometry and sport performance at 1000 meters distance, and how are these relationships going to change based on training period. Methods: To determine statistical dependence between sport performance at 1000 meters distance and choosen factors of sport performance, the correlation research was used - as a variable-dependent value the final result of sport performance at 1000 meters distance was used, as a variable-independent amounts functional parameters values found during kayak spiroergometry were used. To discover the statistical dependence methods of Pearson's correlation coefficient and regression analysis were used. Results: General level of kayak-athletes from testing file indicated by functional parameters values and demonstrated by kayak spiroergometry performance depends on kayak- athlete's level of sport performance at 1000 meters distance in prepared-training period only, when importance for general condition is emphasized. We did not discover the same phenomenon based on pre-racing period testing results. Sport performance at...
6

Estudo da influência de eventos sobre a estrutura do mercado brasileiro de ações a partir de redes ponderadas por correlações de Pearson, Spearman e Kendall / Weighted networks from Pearson, Spearman and Kendall correlations to characterize the influence of events on the Brazilian stock market structure

Origuela, Letícia Aparecida 06 August 2018 (has links)
Neste trabalho foi analisada a influência de um evento sobre o mercado de ações brasileiro a partir das redes, e suas árvores geradoras mínimas, obtidas de medidas de dependência baseadas nas correlações de Pearson, de Spearman e de Kendall. O evento considerado foi a notícia da noite de 17 de maio de 2017 em que o dono da empresa brasileira JBS, Joesley Batista, gravou o então Presidente da República Michel Temer autorizando a compra do silêncio de um Deputado Federal. O dia seguinte a notícia, 18 de maio de 2017, foi definido como o dia do evento. Foram coletados dados de alta frequência de 58 ações do Ibovespa no período de 11 a 25 de maio de 2017. As alterações nas redes das ações do mercado foram analisadas comparando-se o período anterior e posterior ao evento em duas escalas de tempo: (1) Redes diárias: cinco pregões antes do evento, o dia do evento e, cinco pregões depois do evento, com cotações a cada 15 minutos; (2) Agrupadas em antes e depois: agrupando os dados dos 5 dias antes e dos 5 dias depois do evento. O estudo das redes diárias indicou mudança de tendência nas suas propriedades no decorrer do período que contém o evento, com cotações a cada 15 minutos. Isto sugeriu que análise do efeito médio contido nos dados agrupados antes de depois do evento poderiam tornar mais evidente as mudanças na estrutura de rede das ações. As redes antes e depois do evento apresentaram mudanças significativas nas suas métricas que ficaram mais evidenciadas nas árvores geradoras mínimas. As redes geradas pelas correlações de Kendall e Spearman apresentaram um número maior de agrupamentos antes e depois do evento e, após o evento, as árvores geradoras mínimas apresentaram uma redução do número de agrupamentos de ações para todos os tipos de correlação. As distribuições de grau ponderado após o evento indicam uma probabilidade maior de vértices com graus distante da média. As métricas das árvores geradoras mínimas por correlação de Spearman sofreram a maior variação, seguidas pelas de Kendall e Pearson, e também, indicaram que as redes após o evento ficaram mais robustas, ou seja, mais rígidas. A maior robustez das redes após o evento indica maior conectividade do mercado, tornando-o, como um todo, mais suscetível ao impacto de novos acontecimentos. / In this work the influence of an event on the Brazilian stock market was analyzed from networks and its minimum spanning trees obtained from measures of dependence based on the Pearson, Spearman, and Kendall\'s correlations. The event considered was the news in the evening of May 17, 2017 in which the owner of the Brazilian company JBS, Joesley Batista, recorded the Brazilian President Michel Temer authorizing the purchase of the silence of a congress member. The day just after the news, May 18, 2017, was defined as the event day. High-frequency data from 58 Ibovespa shares were collected from 11 to 25 May 2017. Changes in the stocks networks were analyzed comparing the period before and after the event in two time scales: (1) Daily networks: five trade sections before the event, the day of the event and, five trade sections after the event, with price every 15 minutes; (2) Grouped before and after do evento: grouping data from 5 days before and 5 days after event. The study of the daily networks indicated a change of trend in their properties during the period that contains the event, with quotations every 15 minutes. The study of daily networks indicated a change of trend in their properties during the period containing the event. This suggested that analysis of the mean effect of grouped data before and after the event could highlight the changes in the network structure. The networks before and after the event showed significant changes in their metrics, which became more evident from the minimum spanning trees. After the event, the minimum spanning trees for grouped data got a smaller number of clusters in the networks for all kind of correlations. The networks generated by Kendall and Spearman correlations presented a larger number of clusters before and after the event. The weighted degree distributions after the event suggest a power law decay tail for all the correlations considered and indicates a higher probability of vertices with weighted degrees far away from the mean weighted degree. The minimum spanning tree metrics generated by Spearman correlation suffered the greatest variation, followed by those of Kendall and Pearson; and their values indicates that after the event the networks became more robust, that is, more rigid. The increase in the networks robustness after the event indicates a higher market connectivity, making it as a whole, more susceptible to the impact of new events.
7

Estudo da influência de eventos sobre a estrutura do mercado brasileiro de ações a partir de redes ponderadas por correlações de Pearson, Spearman e Kendall / Weighted networks from Pearson, Spearman and Kendall correlations to characterize the influence of events on the Brazilian stock market structure

Letícia Aparecida Origuela 06 August 2018 (has links)
Neste trabalho foi analisada a influência de um evento sobre o mercado de ações brasileiro a partir das redes, e suas árvores geradoras mínimas, obtidas de medidas de dependência baseadas nas correlações de Pearson, de Spearman e de Kendall. O evento considerado foi a notícia da noite de 17 de maio de 2017 em que o dono da empresa brasileira JBS, Joesley Batista, gravou o então Presidente da República Michel Temer autorizando a compra do silêncio de um Deputado Federal. O dia seguinte a notícia, 18 de maio de 2017, foi definido como o dia do evento. Foram coletados dados de alta frequência de 58 ações do Ibovespa no período de 11 a 25 de maio de 2017. As alterações nas redes das ações do mercado foram analisadas comparando-se o período anterior e posterior ao evento em duas escalas de tempo: (1) Redes diárias: cinco pregões antes do evento, o dia do evento e, cinco pregões depois do evento, com cotações a cada 15 minutos; (2) Agrupadas em antes e depois: agrupando os dados dos 5 dias antes e dos 5 dias depois do evento. O estudo das redes diárias indicou mudança de tendência nas suas propriedades no decorrer do período que contém o evento, com cotações a cada 15 minutos. Isto sugeriu que análise do efeito médio contido nos dados agrupados antes de depois do evento poderiam tornar mais evidente as mudanças na estrutura de rede das ações. As redes antes e depois do evento apresentaram mudanças significativas nas suas métricas que ficaram mais evidenciadas nas árvores geradoras mínimas. As redes geradas pelas correlações de Kendall e Spearman apresentaram um número maior de agrupamentos antes e depois do evento e, após o evento, as árvores geradoras mínimas apresentaram uma redução do número de agrupamentos de ações para todos os tipos de correlação. As distribuições de grau ponderado após o evento indicam uma probabilidade maior de vértices com graus distante da média. As métricas das árvores geradoras mínimas por correlação de Spearman sofreram a maior variação, seguidas pelas de Kendall e Pearson, e também, indicaram que as redes após o evento ficaram mais robustas, ou seja, mais rígidas. A maior robustez das redes após o evento indica maior conectividade do mercado, tornando-o, como um todo, mais suscetível ao impacto de novos acontecimentos. / In this work the influence of an event on the Brazilian stock market was analyzed from networks and its minimum spanning trees obtained from measures of dependence based on the Pearson, Spearman, and Kendall\'s correlations. The event considered was the news in the evening of May 17, 2017 in which the owner of the Brazilian company JBS, Joesley Batista, recorded the Brazilian President Michel Temer authorizing the purchase of the silence of a congress member. The day just after the news, May 18, 2017, was defined as the event day. High-frequency data from 58 Ibovespa shares were collected from 11 to 25 May 2017. Changes in the stocks networks were analyzed comparing the period before and after the event in two time scales: (1) Daily networks: five trade sections before the event, the day of the event and, five trade sections after the event, with price every 15 minutes; (2) Grouped before and after do evento: grouping data from 5 days before and 5 days after event. The study of the daily networks indicated a change of trend in their properties during the period that contains the event, with quotations every 15 minutes. The study of daily networks indicated a change of trend in their properties during the period containing the event. This suggested that analysis of the mean effect of grouped data before and after the event could highlight the changes in the network structure. The networks before and after the event showed significant changes in their metrics, which became more evident from the minimum spanning trees. After the event, the minimum spanning trees for grouped data got a smaller number of clusters in the networks for all kind of correlations. The networks generated by Kendall and Spearman correlations presented a larger number of clusters before and after the event. The weighted degree distributions after the event suggest a power law decay tail for all the correlations considered and indicates a higher probability of vertices with weighted degrees far away from the mean weighted degree. The minimum spanning tree metrics generated by Spearman correlation suffered the greatest variation, followed by those of Kendall and Pearson; and their values indicates that after the event the networks became more robust, that is, more rigid. The increase in the networks robustness after the event indicates a higher market connectivity, making it as a whole, more susceptible to the impact of new events.
8

Uplatnění statistických metod při zpracování dat / The Use of Statistical Methods for Data Processing

Čupr, Jiří January 2016 (has links)
This master's thesis is focused on problem of orders of ingredients in McDonald's. It's an analysis of usage changes depending on outside temperature. Thesis includes theoretical background for correct analysis of the problem and possibilities to figuring it out. There is also an algorithmus for more efficient solution of problem with needs or excess of ingredients. There is also a program written in VBA language, that makes more simple usage of this algorithm on restaurants.
9

The public service anti-corruption strategy : a case study for the Department of Correctional Services

Webb, Werner Nicholaas 12 1900 (has links)
The South African Government in 2002 accepted the Public Service Anti-Corruption Strategy (PSACS) with the objective to reduce the manifestation of malfeasance in the public service. The PSACS identified various goals and objectives to be achieved at both the systemic and departmental levels. At the departmental level, the PSACS set out to increase the institutional capacity of departmental institutions, and encourage the management of risk and of discipline in the public service. Departments are required to establish the necessary capacity to formulate fraud prevention and anti-corruption policies, receive and manage allegations of corruption, and investigate allegations of corruption and detected risks at a preliminary level. To manage ethics departments should inter alia identify early signs of a lack of discipline, improve the accountability and capacity of managers to manage discipline, and encourage managers to act against transgressions. However, various authors have been critical of the formulation of policies and the establishment of structures as a policy response to public service corruption. In their view, such an approach often leads to a reduction in the efficiency and effectiveness of public programmes, and even creates opportunities for corruption. In response to such deficiencies, some argue that a compliance-based approach to public service malfeasance should be supplemented by a value-based approach with an emphasis on the development of internal selfcontrol of individuals, the promotion of trust among employees, and the promotion of a culture of responsibility. In this context, this researcher proposes that the promotion of an ethical culture could enhance the implementation of the PSACS. In this dissertation, this researcher set out to evaluate, among others, the ethical culture of the Department of Correctional Services (DCS). It was decided that a survey would be the most appropriate data collection method. A questionnaire was administered and the data was captured, analysed and interpreted. Various statistical tests were performed and the findings suggest inter alia that the promotion of an ethical culture coincides with lower levels of observed malfeasance. Consequently, when greater clarity of operational and ethics policies is obtained, an increase occurs in both the severity and frequency of penalties for malfeasance, and officials gain greater access to resources and time to execute their responsibilities, the level of observed malfeasance is likely to be reduced. The promotion of an ethical culture could significantly enhance the implementation of the PSACS. / Public Administration / D. Litt. et Phil. (Public Administration)
10

Métodos geoestatísticos de co-estimativas: estudo do efeito da correlação entre variáveis na precisão dos resultados / Co-estimation geostatistical methods: a study of the correlation between variables at results precision

Watanabe, Jorge 29 February 2008 (has links)
Esta dissertação de mestrado apresenta os resultados de uma investigação sobre os métodos de co-estimativa comumente utilizados em geoestatística. Estes métodos são: cokrigagem ordinária; cokrigagem colocalizada e krigagem com deriva externa. Além disso, a krigagem ordinária foi considerada apenas a título de ilustração como esse método trabalha quando a variável primária estiver pobremente amostrada. Como sabemos, os métodos de co-estimativa dependem de uma variável secundária amostrada sobre o domínio a ser estimado. Adicionalmente, esta variável deveria apresentar correlação linear com a variável principal ou variável primária. Geralmente, a variável primária é pobremente amostrada enquanto a variável secundária é conhecida sobre todo o domínio a ser estimado. Por exemplo, em exploração petrolífera, a variável primária é a porosidade medida em amostras de rocha retiradas de testemunhos e a variável secundária é a amplitude sísmica derivada de processamento de dados de reflexão sísmica. É importante mencionar que a variável primária e a variável secundária devem apresentar algum grau de correlação. Contudo, nós não sabemos como eles funcionam dependendo do grau de correlação. Esta é a questão. Assim, testamos os métodos de co-estimativa para vários conjuntos de dados apresentando diferentes graus de correlação. Na verdade, esses conjuntos de dados foram gerados em computador baseado em algoritmos de transformação de dados. Cinco valores de correlação foram considerados neste estudo: 0,993, 0,870, 0,752, 0,588 e 0,461. A cokrigagem colocalizada foi o melhor método entre todos testados. Este método tem um filtro interno que é aplicado no cálculo do peso da variável secundária, que por sua vez depende do coeficiente de correlação. De fato, quanto maior o coeficiente de correlação, maior é o peso da variável secundária. Então isso significa que este método funciona mesmo quando o coeficiente de correlação entre a variável primária e a variável secundária é baixo. Este é o resultado mais impressionante desta pesquisa. / This master dissertation presents the results of a survey into co-estimation methods commonly used in geostatistics. These methods are ordinary cokriging, collocated cokriging and kriging with an external drift. Besides that ordinary kriging was considered just to illustrate how it does work when the primary variable is poorly sampled. As we know co-estimation methods depend on a secondary variable sampled over the estimation domain. Moreover, this secondary variable should present linear correlation with the main variable or primary variable. Usually the primary variable is poorly sampled whereas the secondary variable is known over the estimation domain. For instance in oil exploration the primary variable is porosity as measured on rock samples gathered from drill holes and the secondary variable is seismic amplitude derived from processing seismic reflection data. It is important to mention that primary and secondary variables must present some degree of correlation. However, we do not know how they work depending on the correlation coefficient. That is the question. Thus, we have tested co-estimation methods for several data sets presenting different degrees of correlation. Actually, these data sets were generated in computer based on some data transform algorithms. Five correlation values have been considered in this study: 0.993; 0.870; 0.752; 0.588 and 0.461. Collocated simple cokriging was the best method among all tested. This method has an internal filter applied to compute the weight for the secondary variable, which in its turn depends on the correlation coefficient. In fact, the greater the correlation coefficient the greater the weight of secondary variable is. Then it means this method works even when the correlation coefficient between primary and secondary variables is low. This is the most impressive result that came out from this research.

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