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Heteroscedastic latent variable modelling with applications to multivariate statistical process control

Reis, Marco S.; Saraiva, Pedro M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
65.83%
We present an approach for conducting multivariate statistical process control (MSPC) in noisy environments, i.e., when the signal to noise ratio is low, and, furthermore, noise standard deviation (uncertainty) affecting each collected value can vary over time, and is assumingly known. This approach is based upon a latent variable model structure, HLV (standing for heteroscedastic latent variable model), that explicitly integrates information regarding data uncertainty. Moderate amounts of missing data can also be handled in a coherent and fully integrated way through HLV. Several examples show the added value achieved under noisy conditions by adopting such an approach and a case study illustrates its application to a real industrial context of pulp and paper product quality data analysis.; http://www.sciencedirect.com/science/article/B6TFP-4GX1HVW-2/1/c5e6b0a181b2fb4ffd7803ff38c9dace

Exploring the knowledge contained in neuroimages: Statistical discriminant analysis and automatic segmentation of the most significant changes

SANTOS, Paulo E.; THOMAZ, Carlos E.; SANTOS, Danilo dos; FREIRE, Rodolpho; SATO, Joao R.; LOUZA, Mario; SALLET, Paulo; BUSATTO, Geraldo; GATTAZ, Wagner F.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.91%
Objective: The aim of this article is to propose an integrated framework for extracting and describing patterns of disorders from medical images using a combination of linear discriminant analysis and active contour models. Methods: A multivariate statistical methodology was first used to identify the most discriminating hyperplane separating two groups of images (from healthy controls and patients with schizophrenia) contained in the input data. After this, the present work makes explicit the differences found by the multivariate statistical method by subtracting the discriminant models of controls and patients, weighted by the pooled variance between the two groups. A variational level-set technique was used to segment clusters of these differences. We obtain a label of each anatomical change using the Talairach atlas. Results: In this work all the data was analysed simultaneously rather than assuming a priori regions of interest. As a consequence of this, by using active contour models, we were able to obtain regions of interest that were emergent from the data. The results were evaluated using, as gold standard, well-known facts about the neuroanatomical changes related to schizophrenia. Most of the items in the gold standard was covered in our result set. Conclusions: We argue that such investigation provides a suitable framework for characterising the high complexity of magnetic resonance images in schizophrenia as the results obtained indicate a high sensitivity rate with respect to the gold standard. (C) 2010 Elsevier B.V. All rights reserved.; FAPESP; SP; CNPq...

Avaliação de alterações em redes de drenagem de microbacias como subsídio ao zoneamento geoambiental de bacias hidrográficas: aplicação na bacia hidrográfica do Rio Capivari - SP.; Alteration evaluation in microbasin drainage systems as a subsidy to the geoenvironmental zoning of hydrographic basins: application in the Capivari river hydrographic basin.

Collares, Eduardo Goulart
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 01/12/2000 PT
Relevância na Pesquisa
65.81%
A rede de drenagem se constitui em importante indicador de alterações ocorridas na composição da paisagem de bacias hidrográficas, seja por mudanças na sua estruturação, forma ou então por ganho ou perda de canais. O objetivo deste trabalho é apresentar e aplicar uma proposta metodológica, com base em análise morfométrica temporal das redes de drenagem de microbacias, visando a avaliação das alterações e o zoneamento regional de uma bacia hidrográfica. A metodologia envolve o uso de imagens de sensoriamento remoto e técnicas de geoprocessamento para a caracterização das atividades antrópicas e levantamento das variáveis morfométricas em duas datas, com um intervalo de 23 anos. A avaliação das alterações e a consequente classificação das microbacias são efetuadas com base em análise estatística multivariada. A proposta foi aplicada na bacia hidrográfica do rio Capivari e os resultados comprovam que ocorreram alterações significativas na composição da rede de drenagem no período de análise. As variáveis morfométricas que mais contribuíram para a avaliação das alterações foram a Densidade de Drenagem e Densidade Hidrográfica. Dentre as microbacias que mais se alteraram estão as urbanas ou em processo de urbanização e...

A utilização do processo de avaliação on-line como apoio ao ensino presencial: desenvolvimento e análise junto ao laboratório virtual de estatística aplicada à administração - LaViE; Online evaluation process used as support to presencial teaching : development and analysis at the virtual laboratory of statistics applied to business management - LaViE

Marques, Érica Ferreira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 16/04/2007 PT
Relevância na Pesquisa
75.9%
As dificuldades de aprendizagem sobre estatística e suas aplicações simplesmente em razão da matemática envolvida, principalmente, pelos alunos dos cursos de humanas, fazem dela um desafio para o professor que a ministra e também para o aluno que aprende. Assim, esta tese busca mostrar o quanto à elaboração e o desenvolvimento de uma ferramenta de avaliação tipo teste em um ambiente virtual pode contribuir como apoio ao ensino presencial do estudo de ferramentas estatísticas multivariadas para os alunos de graduação em Administração da FEARP/USP, matriculados na disciplina Estatística Aplicada à Administração II. Este trabalho faz parte do projeto virtual denominado LaViE, que é um ambiente virtual de ensino-aprendizagem de estatística, e que está fundamentado em três dimensões: Pedagogia Virtual, Tecnologia da Comunicação e Processo de Validação. Para a criação dessa ferramenta de avaliação tipo teste online foi necessário, primeiramente, a elaboração de um protocolo para desenvolvimento e implementação desse sistema no LaViE. A metodologia, então, foi baseada em três etapas: 1) elaboração do protocolo fundamentado na pesquisa exploratória de pedagogia virtual com base na teoria sobre processo de ensino-aprendizagem para o desenvolvimento de um conjunto de regras e passos que balizasse a criação de questões testes on-line com níveis diferentes de ?adaptação? pelo aluno para cada módulo apresentado na disciplina em questão. Neste caso...

Caracterização de tecidos mamários através de modelos estatísticos utilizando o espalhamento de raios-x".; Breast Tissue Characterization by Statistical Models Using X-Ray Scattering

Cunha, Diego Merigue da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 24/03/2006 PT
Relevância na Pesquisa
65.89%
Em um exame mamográfico, quando os fótons de raios-X incidem sobre a mama, uma parte destes fótons é transmitida sem ser desviada da trajetória inicial (radiação transmitida primária), permitindo a formação da imagem mamográfica, e outra é dispersa de sua trajetória inicial pelo tecido (radiação espalhada), atuando de forma deletéria na imagem mamográfica. Entretanto, recentes investigações têm demonstrado que a radiação espalhada pode ser útil na caracterização de tecidos. O objetivo deste trabalho é desenvolver um modelo de diagnóstico de alterações no tecido mamário utilizando as informações presentes na distribuição angular da radiação espalhada (perfil de espalhamento). Os perfis de espalhamento de 40 amostras de tecidos mamários foram obtidos utilizando um difractômetro comercial SIEMENS D5005, operando em modo reflexão na energia de 8,04 keV e variando o detector da posição angular de 5º a 150º, correspondendo a um intervalo de x de 0,03Å-1 a 0,62 Å-1. As amostras de tecido foram previamente classificadas histopatologicamente como tecidos normais, fibroadenomas (neoplasias benignas) e diferentes tipos de carcinomas (neoplasias malignas). Neste trabalho, três modelos de diagnóstico baseados na análise estatística dos perfis de espalhamento foram desenvolvidos. O primeiro...

Avaliação do efeito da piscicultura em sistemas aquáticos em Assis e Cândido Mota, São Paulo, por indicador de qualidade da água e análise estatítica multivariada

Simões, Fabiano dos Santos; Yabe, Maria Josefa dos Santos; Moreira, Altair Benedito; Bisinoti, Márcia Cristina
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: 1835-1841
POR
Relevância na Pesquisa
65.78%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); In this work, the impact of fish farming activities on the Queixada, Macuco and Pari-Veado Rivers in the Paranapanema watershed was evaluated. Physical, chemical and microbiological parameters were quantified in these aquatic systems followed by application of multivariate statistical analysis (MSA) and water quality index (WQI) tools. Watersheds where fish farming activities are predominant presented WQI > 52 indicating good quality, whereas MSA demonstrated bad quality for these aquatic bodies. The results showed that the degradation in this watershed follows the fish farming activity. The MSA index is more restricted than the National Foundation Sanitation (NFS) index routinely used to infer water quality.

Avaliação dos aspectos texturais na imagem Landsat como subsídio à compartimentação fisiográfica dos municípios de Peruíbe e Itanhaém - SP

Moreira, Mirley Ribeiro
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: vi, 129 f. : il., tabs.
POR
Relevância na Pesquisa
65.83%
Pós-graduação em Geociências e Meio Ambiente - IGCE; As imagens de satélite, por serem um registro de alvos com diferentes comportamentos espectrais e diferentes arranjos espaciais, respondem com variações tonais de cinza e variações texturais. Esta variação textural é analisada normalmente através de interpretação visual, que é uma sistematização de várias técnicas, as quais convergem para um único objetivo, a compartimentação da imagem. Em geral, a textura apresenta-se como sendo uma arma valiosa na interpretação de formas de relevo, drenagem e de padrões da cobertura vegetal e de uso da terra. Acredita-se que, a partir da utilização das técnicas de processamento digital de imagens e técnicas estatísticas multivariadas, como subsidiária na redução do caráter subjetivo da análise textural e da correspondência entre zonas homólogas, será possível favorecer a discriminação de elementos imageados, e encontrar um modelo que possibilite explicar mais satisfatoriamente a compartimentação e a relação de equivalência entre zonas que constituem texturas semelhantes. Desta forma, o objetivo geral do trabalho, é avaliar diversas metodologias, com intuito de realizar uma compartimentação fisiográfica...

Combining Statistical Methodologies in Water Quality Monitoring in a Hydrological Basin - Space and Time Approaches

Costa, Marco; A. Manuela Gonçalves
Fonte: Intech Publicador: Intech
Tipo: Parte de Livro
ENG
Relevância na Pesquisa
65.84%
In this work are discussed some statistical approaches that combine multivariate statistical techniques and time series analysis in order to describe and model spatial patterns and temporal evolution by observing hydrological series of water quality variables recorded in time and space. These approaches are illustrated with a data set collected in the River Ave hydrological basin located in the Northwest region of Portugal.

Influence of Aveiro Lagoon heavy metal contents in the adjacent continental shelf (Portugal); Influencia de la Laguna de Aveiro en los contenidos de metales pesados en la plataforma continental adyacente (Portugal)

Abrantes, I.; Rocha, F.; Vidinha, J.; Dias, J. A.
Fonte: Universidad Autónoma de Baja California Publicador: Universidad Autónoma de Baja California
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.81%
A chemical analysis of Al, Ca, Fe, Mg, Cu, Pb, Zn, Cr, Co, Ni and Cd was carried out in 22 surface sediment samples of the continental shelf and upper slope between Espinho and Aveiro (Portugal). To reduce the disturbing effects of grain size, all samples were size-normalized by wet sieving (<63 µm). The fine fraction was digested with concentrated acids and analyzed by flame atomic absorption spectrometry. The Al and heavy metal concentrations displayed a similar distribution pattern, decreasing seaward. Exceptions to this general pattern are Ca, Mg and Pb distributions. The Ca contents are related to carbonated biogenic particles that are very abundant in the outer shelf. Multivariate statistical analysis was applied to all data to assess the behaviour and sources of each element analyzed. The results from factor analysis showed that terrigenous supply (from Aveiro Lagoon flow, coastal erosion and littoral drift), grain size (clay) sorting and anthropogenic influences from Aveiro Lagoon are the major factors controlling spatial variations of chemical elements in the continental shelf between Espinho and Aveiro. Unusually high contents of Pb were found in the middle shelf off Furadouro, but we could not determine the possible source of this contamination.; Se realizaron análisis químicos de Al...

Avaliação do efeito da piscicultura em sistemas aquáticos em Assis e Cândido Mota, São Paulo, por indicador de qualidade da água e análise estatítica multivariada

Simões,Fabiano dos Santos; Yabe,Maria Josefa dos Santos; Moreira,Altair B.; Bisinoti,Márcia Cristina
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 PT
Relevância na Pesquisa
65.78%
In this work, the impact of fish farming activities on the Queixada, Macuco and Pari-Veado Rivers in the Paranapanema watershed was evaluated. Physical, chemical and microbiological parameters were quantified in these aquatic systems followed by application of multivariate statistical analysis (MSA) and water quality index (WQI) tools. Watersheds where fish farming activities are predominant presented WQI > 52 indicating good quality, whereas MSA demonstrated bad quality for these aquatic bodies. The results showed that the degradation in this watershed follows the fish farming activity. The MSA index is more restricted than the "National Foundation Sanitation" (NFS) index routinely used to infer water quality.

Average mass scan of the total ion chromatogram versus percentage chemical composition in multivariate statistical comparison of complex volatile mixtures

Radulović,Niko S.; Blagojević,Polina D.; Skropeta,Danielle
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2010 EN
Relevância na Pesquisa
85.97%
The analysis of complex volatile mixtures by gas chromatography-mass spectrometry (GC-MS) is a time-consuming process. It involves separation and identification of the components based on their retention times and fragmentation patterns, followed by determination of their relative percentages from integration of their peak areas. Herein we show that multivariate statistical analysis of the relative abundances of the m/z values obtained from the average mass scans (AMS) of the complex mixture is a faster and potentially more reliable method of assessing these mixtures. To achieve this, 15 model complex mixtures, were prepared comprising varying amounts of 10 different constituents. The AMS profile and chemical composition of each mixture were compared to one another using agglomerative hierarchical cluster analysis and principal component analysis. The results obtained strongly suggest that multivariate statistical analysis of AMS profiles is a promising, time saving and reliable tool for analyzing complex volatile mixtures, in particular essential oils.

A multivariate statistical analysis of the QSAR of 2-(substituted phenyl)indan-1,3-diones with hypolipidemic activity

Silva,Aluizio G. da; Ramos,Mozart N.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2012 EN
Relevância na Pesquisa
95.91%
Electronic descriptors obtained from AM1 molecular orbital calculations were employed, along with the empirical parameters log P and π, in a multivariate statistical analysis of the quantitative structure-activity relationships (QSAR) in a group of sixteen 2-(substituted phenyl)indan- 1,3-diones possessing hypolipidemic activities. AM1 descriptors were obtained both for the isolated molecule model and, to simulate the solvent effect, for the COSMO model (conductor-like screening model) in our QSAR analysis. From sixteen studied derivatives, three were excluded from the set of molecules used in the model building stage in order to serve as a test set. In general, the results obtained from this test set validated our quantitative models, which were based on linear regressions and principal component analysis (PCA). From these results, new derivatives were predicted to be more potent hypolipidemic agents than the indan-1,3-diones for which experimental activities were determined. For instance, our results suggest that 2-(ortho-hydroxy-phenyl)indan-1,3-dione is a potential candidate for new experimental screening studies for reducing serum cholesterol and triglyceride levels.

Evaluation via multivariate techniques of scale factor variability in the rietveld method applied to quantitative phase analysis with X ray powder diffraction

Oliveira,Terezinha Ferreira de; Avillez,Roberto Ribeiro de; Epprecht,Eugenio Kahn; Queiroz,Joaquim Carlos Barbosa
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 EN
Relevância na Pesquisa
75.87%
The present work uses multivariate statistical analysis as a form of establishing the main sources of error in the Quantitative Phase Analysis (QPA) using the Rietveld method. The quantitative determination of crystalline phases using x ray powder diffraction is a complex measurement process whose results are influenced by several factors. Ternary mixtures of Al2O3, MgO and NiO were prepared under controlled conditions and the diffractions were obtained using the Bragg-Brentano geometric arrangement. It was possible to establish four sources of critical variations: the experimental absorption and the scale factor of NiO, which is the phase with the greatest linear absorption coefficient of the ternary mixture; the instrumental characteristics represented by mechanical errors of the goniometer and sample displacement; the other two phases (Al2O3 and MgO); and the temperature and relative humidity of the air in the laboratory. The error sources excessively impair the QPA with the Rietveld method. Therefore it becomes necessary to control them during the measurement procedure.

Batch-to-Batch Quality Consistency Evaluation of Botanical Drug Products Using Multivariate Statistical Analysis of the Chromatographic Fingerprint

Xiong, Haoshu; Yu, Lawrence X.; Qu, Haibin
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Publicado em 02/05/2013 EN
Relevância na Pesquisa
65.99%
Botanical drug products have batch-to-batch quality variability due to botanical raw materials and the current manufacturing process. The rational evaluation and control of product quality consistency are essential to ensure the efficacy and safety. Chromatographic fingerprinting is an important and widely used tool to characterize the chemical composition of botanical drug products. Multivariate statistical analysis has showed its efficacy and applicability in the quality evaluation of many kinds of industrial products. In this paper, the combined use of multivariate statistical analysis and chromatographic fingerprinting is presented here to evaluate batch-to-batch quality consistency of botanical drug products. A typical botanical drug product in China, Shenmai injection, was selected as the example to demonstrate the feasibility of this approach. The high-performance liquid chromatographic fingerprint data of historical batches were collected from a traditional Chinese medicine manufacturing factory. Characteristic peaks were weighted by their variability among production batches. A principal component analysis model was established after outliers were modified or removed. Multivariate (Hotelling T2 and DModX) control charts were finally successfully applied to evaluate the quality consistency. The results suggest useful applications for a combination of multivariate statistical analysis with chromatographic fingerprinting in batch-to-batch quality consistency evaluation for the manufacture of botanical drug products.

Rapid detection of nasopharyngeal cancer using Raman spectroscopy and multivariate statistical analysis

LI, YONGZENG; HUANG, WEI; PAN, JIANJI; YE, QING; LIN, SHAOJUN; FENG, SHANGYUAN; XIE, SHUSEN; ZENG, HAISHAN; CHEN, RONG
Fonte: D.A. Spandidos Publicador: D.A. Spandidos
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
65.82%
Optical spectroscopic techniques, including Raman spectroscopy, have shown promise for in vivo cancer diagnostics in a variety of organs. In this study, the potential use of a home-made Raman spectral system with a millimeter order excitation laser spot size combined with a multivariate statistical analysis for the rapid detection and discrimination of nasopharyngeal cancer from normal nasopharyngeal tissue was evaluated. Raman scattering signals were acquired from 16 normal and 32 nasopharyngeal carcinoma tissue samples. Linear discriminant analysis (LDA) based on principal component analysis (PCA) and partial least squares (PLS) were employed to generate diagnostic algorithms for the classification of different nasopharyngeal tissue types. Spectral differences in Raman spectra between the two types of tissues were revealed; the normalized intensities of Raman peaks at 1,001, 1,207 and 1,658 cm−1 were more intense for nasopharyngeal carcinoma tissue compared to normal tissue, while Raman bands at 848, 936 and 1,446 cm−1 were stronger in normal nasopharyngeal samples. The PCA-LDA algorithm together with leave-one-out cross validation yields a diagnostic sensitivity of 81% and a specificity of 87%, while the PLS method coupled with subwindow permutation analysis improves the diagnostic sensitivity and specificity to 85 and 88%...

Characterization of aromatic profiles in brazilian tropical wines determined by gas chromatography and multivariate statistical analysis.

ARAÚJO, A. J. de B.; VANDERLINDE, R.; LIMA, L. L. de A.; PEREIRA, G. E.
Fonte: In: INTERNATIONAL SYMPOSIUM OF THE GROUP OF INTERNATIONAL EXPERTS OF VITIVINICULTURAL SYSTEMS FOR COOPERATION, 17., 2011, Asti. Proceedings... Asti: Le Progrès Agricole et Viticole, 2011. Publicador: In: INTERNATIONAL SYMPOSIUM OF THE GROUP OF INTERNATIONAL EXPERTS OF VITIVINICULTURAL SYSTEMS FOR COOPERATION, 17., 2011, Asti. Proceedings... Asti: Le Progrès Agricole et Viticole, 2011.
Tipo: Artigo em anais de congresso (ALICE) Formato: p. 49-51.
EN
Relevância na Pesquisa
65.87%
Tropical wines have been produced in Thailand, India, Venezuela and mainly in Northeastem Brazil. In Brazil, this activity started twenty-five years ago and has been studied only in the last years. In this Brazilian Area, between 8_90 parallel of the South Hemisphere, it is possible to have two or three harvests per year due to the high temperatures (annual average temperature of 26 "C), high luminosity and use of irrigation. Analytical composition of grapes and wines can vary strongly according to harvest date into a year, (wines elaborated in the first or second semester). The aim of this work was to determine metabolic fingerprints of white and red wines from two vintages of 2009, according to their aromatic profile, using gas chromatographyand multivariate statistical analyses. Wines were elaborated by traditional methods, in stainless steel tanks of 200 L, by controlling fermentations temperature for red and white wines and using antioxidants. After stabilization and bottling, wines were analyzed in triplicate using gas chromatography with flame ionization detecto r (OC-FID). PCA multivariate statistical analysis was applied on aromatic compounds data to discriminate between wine type and month of winemaking, and different clustering were formed. White and red tropical wines presented different aromatic compound concentrations; higher alcohols were more efficient to separate wine samples than volatile esters.; 2011

Multivariate Statistical Analysis as a Supplementary Tool for Interpretation of Variations in Salivary Cortisol Level in Women with Major Depressive Disorder

Dziurkowska, Ewelina; Wesolowski, Marek
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
65.94%
Multivariate statistical analysis is widely used in medical studies as a profitable tool facilitating diagnosis of some diseases, for instance, cancer, allergy, pneumonia, or Alzheimer's and psychiatric diseases. Taking this in consideration, the aim of this study was to use two multivariate techniques, hierarchical cluster analysis (HCA) and principal component analysis (PCA), to disclose the relationship between the drugs used in the therapy of major depressive disorder and the salivary cortisol level and the period of hospitalization. The cortisol contents in saliva of depressed women were quantified by HPLC with UV detection day-to-day during the whole period of hospitalization. A data set with 16 variables (e.g., the patients' age, multiplicity and period of hospitalization, initial and final cortisol level, highest and lowest hormone level, mean contents, and medians) characterizing 97 subjects was used for HCA and PCA calculations. Multivariate statistical analysis reveals that various groups of antidepressants affect at the varying degree the salivary cortisol level. The SSRIs, SNRIs, and the polypragmasy reduce most effectively the hormone secretion. Thus, both unsupervised pattern recognition methods, HCA and PCA, can be used as complementary tools for interpretation of the results obtained by laboratory diagnostic methods.

Multivariate Statistical Analysis: A Geometric Perspective

Tyurin, Yuri N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/02/2009
Relevância na Pesquisa
65.97%
A new, coordinate-free (geometric) approach to multivariate statistical analysis. General multivariate linear models and linear hypotheses are defined in geometric form. A method of constructing statistical criteria is defined for linear hypotheses. As a result, multivariate statistical analysis is developed in full analogy to classical statistical analysis. This approach is based on tensor products and modules over the ring of square matrices, supplied with an inner product.; Comment: 25 pages

Trace element distribution in human teeth by x-ray fluorescence spectrometry and multivariate statistical analysis

Oprea, Cristiana; Szalanski, Pavel J.; Gustova, Marina V.; Oprea, Ioan A.; Buzguta, Violeta L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/06/2014
Relevância na Pesquisa
65.8%
X-ray fluorescence spectrometry (XRFS) was used as a multielement method of evaluation of individual whole human tooth or tooth tissues for their amounts of trace elements. Measurements were carried out on human enamel, dentine, and dental cementum, and some differences in tooth matrix composition were noted. In addition, the elemental concentrations determined in teeth from subjects of different ages, nutritional states, professions and gender, living under various environmental conditions and dietary habits, were included in a comparison by multivariate statistical analysis (MVSA) methods. By factor analysis it was established that inorganic components of human teeth varied consistently with their source in the tissue, with more in such tissue from females than in that from males, and more in tooth incisor than in tooth molar.

Using multivariate statistical analysis to assess changes in water chemistry in sections of the Vaal Dam catchment between 1991 and 2008

Bird,Theresa L; Scholes,Mary C
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
Relevância na Pesquisa
75.87%
Multivariate statistical analysis was used to investigate changes in water chemistry at 5 river sites in the Vaal Dam catchment, draining the Highveld grasslands. These grasslands receive more than 8 kg sulphur (S) ha-1-year-1 and 6 kg nitrogen (N) ha-1-year-1 via atmospheric deposition. It was hypothesised that between 1991 and 2008 concentrations of dissolved mineral salts, sulphate, nitrate and ammonium would increase as a result of the S and N deposition received. Significant spatial differences were found, by analysis of covariance, between sites within the catchment. Canonical correspondence analysis (CCA) showed that the environmental variables used in the analysis, discharge and month of sampling, explained a small proportion of the total variance in the data set - less than 10% at each site. However, the total data set variance, explained by the 4 hypothetical axes generated by the CCA was >93% for all 5 sites. Sulphate, nitrate-plus-nitrite, ammonium and phosphate concentrations increased at 1 site each, between 1991 and 2008. Over the same time frame, acid-neutralising capacity was decreased significantly at 1 of the 5 river sites. The concentrations of the ions analysed, with rare exception, were within the limits set by the national drinking water guidelines...