| 1. |
- Artursson, Tom, et al.
(författare)
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Drift correction for gas sensors using multivariate methods
- 2000
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Ingår i: Journal of Chemometrics. - 0886-9383 .- 1099-128X. ; 14:5-6, s. 711-723
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Tidskriftsartikel (refereegranskat)abstract
- Drift is one of the most serious impairments afflicting gas sensors. It can be seen as a gradual change in the sensor response over a long period of time when the external conditions an constant. This paper presents a new simple drift counteraction method based on PCA and PLS. The basic idea is to remove the drift direction component from the measurements. The direction of the drift, p, is calculated from measurements for a reference gas. Projecting the sample gas measurements on this vector gives the score vector t. The drift component tp(T) can then he removed from the sample gas data, which we call component correction (CC). The method is tested on a data set based on a reduced factorial design with four gases and a concentration gradient of hydrogen. It is found that the method works efficiently for both cases. Copyright (C) 2000 John Wiley & Sons, Ltd.
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| 2. |
- Andersson, Per M, et al.
(författare)
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Comparison between physicochemical and calculated molecular descriptors
- 2000
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Ingår i: Journal of Chemometrics: Special Issue: Proceedings of the SSC6, August 1999, HiT/TF, Norway . Issue Edited by Kim Esbensen. ; 14:5-6, s. 629-42
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Tidskriftsartikel (refereegranskat)abstract
- It has earlier been proven that measured physicochemical properties are useful in the selection of building blocks for combinatorial chemistry as well as for investigation of the scope and limitations of organic reactions. However, measured physicochemical properties are only available for small subsets of reagents, starting materials or building blocks; therefore it is necessary to use calculated descriptors and it is essential that the descriptors are relevant. The objective was to investigate whether three different descriptor data sets contained similar information about the chemical structure, with the major aim to investigate whether calculated descriptors contain similar information as experimental data. A total of 205 heterogeneous primary amines were characterized using three different data sets of molecular descriptor variables. The first set consisted of four physicochemical variables compiled from the literature and commercially available chemicals in chemical catalogues. From these four descriptors together with molecular weight, three additional descriptors could be calculated, resulting in a total of eight descriptor variables in the first data set. The second data set consisted of 81 calculated molecular descriptor variables relating to size, connectivity, atom count, topology and electrotopology indices. The third data set consisted of 10 semi-empirical variables (AM1). All the calculated variables were generated using the software Tsar 3.11. The descriptor variable sets were compared using principal component analysis (PCA) and partial least squares projections to latent structures (PLS). The following result shows that the different descriptor sets do contain similar latent information and that the different types of calculated variables do correlate well with the experimental data, making them suitable to use for e.g. combinatorial library design.
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| 3. |
- Antti, Henrik, et al.
(författare)
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Detection of kappa number distributions in kraft pulps using nir spectroscopy and multivariate calibration
- 2000
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Ingår i: TAPPI Journal. ; 83:3, s. 102-8
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Tidskriftsartikel (refereegranskat)abstract
- Chemical pulp is characterized by its average lignin content, commonly expressed as the pulp-kappa number. However, this average kappa number provides no information about the distribution of kappa number within the pulp . This study proposes a new method of pulp characterization using near-infrared reflectance (NIR) spectroscopy to measure distributions of kappa numbers within pulp samples. Pure pulps with different kappa numbers were mixed to create blended samples with a known nonuniformity of kappa number distribution. NIR spectroscopy-combined with multi-variate calibration methods was used to detect distributions of kappa numbers in the pulps. Models calculated from these data gave good predictions of the average kappa number as well as the standard deviation around the average. The results imply that NIR spectroscopy can provide information about the average kappa number as well as the distribution of kappa number within the pulp.
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| 4. |
- Ekwall, Björn, et al.
(författare)
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MEIC evaluation of acute systemic toxicity : Part VIII. Multivariate partial least squares evaluation, including the selection of a battery of cell line tests with a good prediction of human acute lethal peak blood concentrations for 50 chemicals
- 2000
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Ingår i: Atla-Alternatives to Laboratory Animals. - 0261-1929. ; 28, s. 201-34
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Tidskriftsartikel (refereegranskat)abstract
- The Multicenter Evaluation of In vitro Cytotoxicity (MEIC) programme was set up to evaluate the relevance for human acute toxicity of in vitro cytotoxicity tests. A total of 61 assays were used to test all 50 reference chemicals. The results of all the tests and the human database were presented in the first five papers of this series. An evaluation of the relevance for human acute toxicity of all submitted test results with use of hard linear regression modelling was presented in the next two papers, and demonstrated a high relevance of in vitro tests, notably tests involving human cell lines. In the present study, multivariate partial least square (PLS) modelling with latent variables analysis has been used to reach two objectives. The first objective was to study the prediction of human acute toxicity by the 61 assays. The second objective was to select a practical battery from the 61 assays, with an optimal prediction of lethal blood concentrations from human acute poisonings of the chemicals. A two-component PLS model of all 61 assays predicted three sets of lethal blood concentrations (clinical, forensic and peak concentrations) very well (R-2 = 0.77, 0.76 and 0.83, Q(2) = 0.74, 0.72 and 0.81, respectively), providing correlative evidence for a high relevance for human acute toxicity of most of the assays. The assays with human cells were highly predictive, whereas assays with Very short incubation times and non-fish ecotoxicological assays were least predictive. These findings confirm the previous results from linear regression analysis. To select an optimal battery, 24 successive PLS models of in vitro data were compared with lethal peak concentrations. The battery selection was based on 38 chemicals with reliable and relevant lethal peak concentrations. An initial PLS model of all 61 assays was used to select the 15 most predictive and most distinct assays. Subsequent PLS models were used to measure the decrease in prediction when assays were deleted from the 15-test battery, as well as the increase in prediction when some extra-predictive assays (as identified by the deletion process) were added later to an optimal two-test battery. The most predictive three-test battery (R-2 = 0.79 and Q(2) = 0.78 for all 50 chemicals) included two circumstantial assays. The most predictive and most cost-effective battery consisted of three human cell line assays, with four endpoints and two exposure times, i.e. protein content (24 hours), ATP content (24 hours), inhibition of elongation of cells (24 hours), and pH-change (7 days). This 1, 5, 9, 16 battery exclusively measures basal cytotoxicity, and is highly predictive (R-2 = 0.77 and Q(2) = 0.76 for 50 chemicals) of the actual lethal peak blood concentrations from acute poisonings in humans. The battery prediction compares favourably with the prediction of human lethal dose by a PLS model of rat and mouse 50% lethal dose (LD50) values for the 50 chemicals (R-2 = 0.65 and Q(2) = 0.64). The three assays of the battery and other promising MEIC assays should be formally validated as soon as possible. The battery can be used immediately for several non-regulatory purposes, including the high-throughput screening of potential pharmaceuticals.
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| 5. |
- Héberger, K., et al.
(författare)
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Partial least squares modeling of retention data of oxo compounds in gas chromatography
- 2000
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Ingår i: Chromatographia. - 0009-5893 .- 1612-1112. ; 51:9-10, s. 595-600
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Tidskriftsartikel (refereegranskat)abstract
- Partial least squares modeling of latent structures were carried out on a data matrix consisting of Kováts retention indices of 35 aliphatic ketones and aldehydes and their physical characteristics. The retention indices were determined on capillary columns with 4 different stationary phases, namely bonded methyl-{HP-1}, methyl-phenyl- {HP-50} and trifluoropropyl-methyl siloxane {DB-210}, as well as polyethylene glycol {HP-Innovax} at four different temperatures. It was found that ketones and aldehydes cannot be classified on the basis of retention data solely, whereas the physical characteristics (boiling point, molar volume, molecular mass, molar refraction, octanol-water partition coefficient) contain the necessary information for differentiation of the two classes of compounds. The retention index of but-2-enal does not fit into the general trend of aliphatic aldyhydes and ketones. A predictive PLS model was built to estimate retention data of oxo compounds at different temperatures and various stationary phases of different polarity. Cross-validation suggests a good reliability of the results. Characteristic plots (PLS weights, scores) show the similar retention behavior of oxo compounds (Figures 3 and 4).
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| 6. |
- Uppgård, Lise-Lott, 1970-, et al.
(författare)
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Multivariate quantitative structure-activity relationships for the aquatic toxicity of alkyl polyglucosides
- 2000
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Ingår i: Tenside Surfactants Detergents. ; 37:2, s. 131-8
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Tidskriftsartikel (refereegranskat)abstract
- The aquatic toxicity of 34 alkyl polyglucosides (APGs) towards two fresh-water species, Thamnocephalus platyurus and Brachionus calyciflorus were studied. The toxicity tests were performed using so-called toxkits, and for each surfactant the results are presented as (10)log (mean LC50) values. The toxicity data were combined with physico-chemical data for the APGs, and a Multivariate Quantitative Structure-Activity Relationship (M-QSAR) model was calculated. Partial Least Squares (PLS) regression was used to develop the M-QSAR model. The resulting linear M-QSAR model explained 93.6% of the variance in the biological response and had a predictability of 86.6% according to cross-validation. The physico-chemical properties with the strongest influences on the toxicity of the surfactants were the critical micelle concentration (c.m.c.), wetting, contact angle, and number of carbon atoms in their hydrophobic parts (C and redC).
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| 7. |
- Uppgård, Lise-Lott, 1970-, et al.
(författare)
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Multivariate quantitative structure-activity relationships for the aquatic toxicity of technical nonionic surfactants
- 2000
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Ingår i: Journal of Surfactants and Detergents. - : Wiley. - 1097-3958 .- 1558-9293. ; 3:1, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- The aquatic toxicity of 36 technical nonionic surfactants (ethoxylated fatty alcohols) was examined toward two freshwater animal species, the fairy shrimp Thamnocephalus playtyurus and the rotifer Brachionus calyciflorus. Responses of the two species to the surfactants were generally similar. A multivariate-quantitative structure-activity relationship (M-QSAR) model was developed from the data. The M-QSAR model consisted of a partial least squares model with three components and explained 92.4% of the response variance and had a predictive capability of 89.1%. The most important physicochemical variables for the M-QSAR model were the number of carbon atoms in the longest chain of the surfactant hydrophobe (redC), the molecular hydrophobicity (log P), the number of carbon atoms in the hydrophobe (C), the hydrophilic-lipophilic balance according to Davis (Davis), the critical packing parameter with respect to whether the hydrophobe was branched or not (redCPP), and the critical micelle concentration. Surfactant toxicity tended to increase with increasing alkyl chain lengths.
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