Search results for "principal"
showing 10 items of 795 documents
Occurrence of polybrominated diphenyl ethers, perfluorinated compounds, and nonsteroidal anti-inflammatory drugs in freshwater mussels from Latvia.
2018
Abstract The occurrence of polybrominated diphenyl ethers (PBDE), perfluorinated compounds (PFC), and nonsteroidal anti-inflammatory drugs (NSAID) in Latvian freshwater ecosystems was evaluated by using filter-feeding mussels as bioindicators. Twenty four samples of mussels were collected from freshwater bodies throughout the territory of Latvia during the summer of 2017. PBDE contamination was ubiquitous, reaching the highest total concentration of 193.2 pg g−1 w.w. BDE-209 was the most abundant compound, followed by penta-BDE components BDE-49, -100, −99, −153, −154, and −47 in decreasing order. The levels of PFCs in Latvian mussels were generally lower than those reported from other regi…
Use of an artificial model of monitoring data to aid interpretation of principal component analysis
2000
Abstract An artificial data matrix of element concentrations at sampling locations was created which included six simulated gradients of correlated variables (Ca+Mg, Ni+V, Pb+Cu+Zn, Cd, Fe and K), representing a simplified model of a National survey. The data matrix model was used to explore the efficiency with which Principal Components Analysis (PCA), without and with Varimax rotation, could derive the imposed gradients. The dependence of PCA on outliers was decreased by log-transformation of data. The Components derived from non-rotated PCA were confounded by bipolar clusters and oblique gradients, both resulting in superimposition of two independent gradients on one Component. Therefore…
Multivariate Correlation between Analytical Data for Various Organics Dissolved during Autohydrolysis of Silver Birch (Betula pendula) Chips and Trea…
2014
Autohydrolysis pre-treatments were performed for the production of hemicellulose-rich autohydrolysates from silver birch (Betula pendula) chips prior to chemical pulping. Pre-treatment conditions were varied with respect to time (from 30 to 120 min) and temperature (130 and 150 °C), covering a P-factor range from 10 to 238. Hydrolysates were analyzed in terms of carbohydrates, lignin, volatile organic acids, and furanoic compounds. The analytical data were subjected to various chemometric techniques to establish the relationships between dissolved organic components, hardwood and softwood used in the experiments, and applied pre-treatment conditions. Using this method, differences between t…
Selection of biological and chemical parameters indicating or affecting the vitality of Norway spruce
1991
Abstract Thirty-two young and old Norway spruce trees ( Picea abies (L.) Karst.) showing different degrees of damage were investigated in a forest stand in the Taunus Mountains (FRG). The old trees showed visual symptoms of damage such as discolouration of the needles and needle loss. Over 70 biometric, physiological and chemical parameters were determined for needle and soil samples. Interrelationships between these variables were described by correlation analysis. The most discriminant variables between different groups of trees were found by Fisher weighing. This reduced data set was used for principal component analysis and for the classification of various parameters according to diffe…
Multivariate Correlation between Analysis Data on Dissolved Organic Material from Scots Pine (Pinus sylvestris) Chips and their Autohydrolysis Pre-Tr…
2013
Various chemometric techniques were used to establish the relationship between the autohydrolysis conditions prior to pulping and the chemical compositions of the soluble organic materials removed from Scots pine (Pinus sylvestris) wood chips. The aqueous chip pre-treatments (autohydrolysis) were administered at 130 °C and 150 °C for 30, 60, 90, and 120 min, and the hydrolysates obtained were characterized in terms of total carbohydrates (various mono-, oligo-, and polysaccharides together with uronic acid side groups), volatile acids (acetic and formic acids), lignin, and furans (furfural and 5-(hydroxymethyl)furfural). Based on the analytical data gathered, a relatively accurate model for…
Analysis of enantiomers giving partially overlapped peaks by using different treatments of the chromatographic ultraviolet signals: quantification of…
2001
Abstract Different strategies for the quantification of partially coeluting optical isomers have been investigated. The methods tested are based on the use of different features as the analytical UV signals: peak heights, perpendicular drop areas, first and second derivatives of the chromatograms, peak areas obtained by deconvolution of the overlapped peaks with data fitting optimization, and a multivariate model (principal component regression, PCR). The amphetamine-derivative drug pseudoephedrine was selected as a model compound. For chromatography, LiChrospher 100 RP 18 and a mobile-phase consisting of methanol and a solution of carboxymethyl-β-cyclodextrin (the chiral selector) were use…
Penalization and data reduction of auxiliary variables in survey sampling
2012
Survey sampling techniques are quite useful in a way to estimate population parameterssuch as the population total when the large dimensional auxiliary data setis available. This thesis deals with the estimation of population total in presenceof ill-conditioned large data set.In the first chapter, we give some basic definitions that will be used in thelater chapters. The Horvitz-Thompson estimator is defined as an estimator whichdoes not use auxiliary variables. Along with, calibration technique is defined toincorporate the auxiliary variables for sake of improvement in the estimation ofpopulation totals for a fixed sample size.The second chapter is a part of a review article about ridge re…
Can Signaling Theory Help Agency and Resource Scarcity Theories Explain Franchisee Failure? Predicting SBA-Backed Loan Defaults
2010
This study examines the use of analytic techniques to develop a model that predicts the potential default of Small Business Administration (SBA) backed loans issued to American franchisees. Data collected by World Franchising (WF) in their 2008 survey and by SBA from 2000-2008, covering 271 diverse US franchise chains, on the reported failure rates and charge off percentages of SBA backed loans was used to explore associations between franchisor characteristics and franchisee loan performances. The predictive capability of the derived model was assessed using a data mining technique in which the original data set is split into two different subsets: one for estimation and one for validation…
The atractiveness and competitiveness of tourist destinations: A study on Southern Italian regions
2009
The present paper aims to assess the relative attractiveness of competing tourist destinations on the basis of individual visitors' perceptions regarding a holiday destination. Using the feeling of tourist well-being achieved by individual tourists we evaluate indirectly the competitive ability of the tourist area to offer a compound tourist site attractiveness. The methodology employed here uses individual survey questionnaires on the tourists' evaluation of the quality of tourist facilities and attributes in a given area (the 'regional tourist profile') as the basis for constructing an aggregate expression for the relative attractiveness of that area. Using various multidimensional statis…
Missing Value Estimation for Microarray Data by Bayesian Principal Component Analysis and Iterative Local Least Squares
2013
Published version of an article from the journal: Mathematical Problems in Engineering. Also available from Hindawi: http://dx.doi.org/10.1155/2013/162938 Missing values are prevalent in microarray data, they course negative influence on downstream microarray analyses, and thus they should be estimated from known values. We propose a BPCA-iLLS method, which is an integration of two commonly used missing value estimation methods-Bayesian principal component analysis (BPCA) and local least squares (LLS). The inferior row-average procedure in LLS is replaced with BPCA, and the least squares method is put into an iterative framework. Comparative result shows that the proposed method has obtaine…