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Calibration Methods (calibration + methods)
Kinds of Calibration Methods Selected AbstractsSimultaneous Spectrophotometric Determination of 2-Thiouracil and 2-Mercaptobenzimidazole in Animal Tissue Using Multivariate Calibration Methods: Concerns and Rapid Methods for DetectionJOURNAL OF FOOD SCIENCE, Issue 2 2010Abolghasem Beheshti ABSTRACT:, Two multivariate calibration methods, partial least squares (PLS) and principal component regression (PCR), were applied to the spectrophotometric simultaneous determination of 2-mercaptobenzimidazole (MB) and 2-thiouracil (TU). A genetic algorithm (GA) using partial least squares was successfully utilized as a variable selection method. The concentration model was based on the absorption spectra in the range of 200 to 350 nm for 25 different mixtures of MB and TU. The calibration curve was linear across the concentration range of 1 to 10 ,g mL,1 and 1.5 to 15 ,g mL,1 for MB and TU, respectively. The values of the root mean squares error of prediction (RMSEP) were 0.3984, 0.1066, and 0.0713 for MB and 0.2010, 0.1667, and 0.1115 for TU, which were obtained using PCR, PLS, and GA-PLS, respectively. Finally, the practical applicability of the GA-PLS method was effectively evaluated by the concurrent detection of both analytes in animal tissues. It should also be mentioned that the proposed method is a simple and rapid way that requires no preliminary separation steps and can be used easily for the analysis of these compounds, especially in quality control laboratories. [source] Evaluation of the SWEEP model during high winds on the Columbia Plateau ,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2009G. Feng Abstract A standalone version of the Wind Erosion Prediction System (WEPS) erosion submodel, the Single-event Wind Erosion Evaluation Program (SWEEP), was released in 2007. A limited number of studies exist that have evaluated SWEEP in simulating soil loss subject to different tillage systems under high winds. The objective of this study was to test SWEEP under contrasting tillage systems employed during the summer fallow phase of a winter wheat,summer fallow rotation within eastern Washington. Soil and PM10 (particulate matter ,10 µm in diameter) loss and soil and crop residue characteristics were measured in adjacent fields managed using conventional and undercutter tillage during summer fallow in 2005 and 2006. While differences in soil surface conditions resulted in measured differences in soil and PM10 loss between the tillage treatments, SWEEP failed to simulate any difference in soil or PM10 loss between conventional and undercutter tillage. In fact, the model simulated zero erosion for all high wind events observed over the two years. The reason for the lack of simulated erosion is complex owing to the number of parameters and interaction of these parameters on erosion processes. A possible reason might be overestimation of the threshold friction velocity in SWEEP since friction velocity must exceed the threshold to initiate erosion. Although many input parameters are involved in the estimation of threshold velocity, internal empirical coefficients and equations may affect the simulation. Calibration methods might be useful in adjusting the internal coefficients and empirical equations. Additionally, the lack of uncertainty analysis is an important gap in providing reliable output from this model. Published in 2009 by John Wiley & Sons, Ltd. [source] Comparison of calibration methods for the reconstruction of space-time rainfall fields during a rain enhancement experiment in Southern ItalyENVIRONMETRICS, Issue 7 2009Arianna Orasi Abstract The role of rainfall raingauge observations in calibration of radar derived rainfall estimates is investigated. The final goal is the reconstruction of the rainfall fields over the observed area using both information during a rainfall enhancement experiment. Furthermore, we propose a simple protocol to assess the experiment efficacy. A space-time approach and the use of kriging with external drift are applied and compared. Results are again compared with those one obtained through an ordinary kriging (OK). Data come from a dense raingauge network and a weather radar installed in 1992 for the evaluation of a rain enhancement experiment carried out in Southern Italy. In this paper we report detailed results from one seeding operation carried out on 11 April 1992. The procedure to assess the efficacy of rain enhancement experiment is illustrated for 11 seeding operations. Copyright © 2008 John Wiley & Sons, Ltd. [source] Experience in calibrating the double-hardening constitutive model MonotINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2003M. A. Hicks The Monot double-hardening soil model has previously been implemented within a general purpose finite element algorithm, and used in the analysis of numerous practical problems. This paper reviews experience gained in calibrating Monot to laboratory data and demonstrates how the calibration process may be simplified without detriment to the range of behaviours modelled. It describes Monot's principal features, important governing equations and various calibration methods, including strategies for overconsolidated, cemented and cohesive soils. Based on a critical review of over 30 previous Monot calibrations, for sands and other geomaterials, trends in parameter values have been identified, enabling parameters to be categorized according to their relative importance. It is shown that, for most practical purposes, a maximum of only 5 parameters is needed; for the remaining parameters, standard default values are suggested. Hence, the advanced stress,strain modelling offered by Monot is attainable with a similar number of parameters as would be needed for some simpler, less versatile, models. Copyright © 2003 John Wiley & Sons, Ltd. [source] Impartial graphical comparison of multivariate calibration methods and the harmony/parsimony tradeoffJOURNAL OF CHEMOMETRICS, Issue 11-12 2006Forrest Stout Abstract For multivariate calibration with the relationship y,=,Xb, it is often necessary to determine the degrees of freedom for parsimony consideration and for the error measure root mean square error of calibration (RMSEC). This paper shows that degrees of freedom can be estimated by an effective rank (ER) measure to estimate the model fitting degrees of freedom and the more parsimonious model has the smallest ER. This paper also shows that when such a measure is used on the X-axis, simultaneous graphing of model errors and other regression diagnostics is possible for ridge regression (RR), partial least squares (PLS) and principal component regression (PCR) and thus, a fair comparison between all potential models can be accomplished. The ER approach is general and applicable to other multivariate calibration methods. It is often noted that by selecting variables, more parsimonious models are obtained; typically by multiple linear regression (MLR). By using the ER, the more parsimonious model is graphically shown to not always be the MLR model. Additionally, a harmony measure is proposed that expresses the bias/variance tradeoff for a particular model. By plotting this new measure against the ER, the proper harmony/parsimony tradeoff can be graphically assessed for RR, PCR and PLS. Essentially, pluralistic criteria for fairly valuating and characterizing models are better than a dualistic or a single criterion approach which is the usual tactic. Results are presented using spectral, industrial and quantitative structure activity relationship (QSAR) data. Copyright © 2007 John Wiley & Sons, Ltd. [source] Generalization of rank reduction problems with Wedderburn's formulaJOURNAL OF CHEMOMETRICS, Issue 11 2003Joan Ferré Abstract In first- and second-order calibration methods based on spectroscopic data, the calculation of the space spanned by the spectra of the interferences has been an important research subject for, among many other applications, calculating the net analyte signal and obtaining figures of merit. Recently, many different calculation methods have been introduced. We show that the calculation of this space can be interpreted from a unified point of view, namely from the rank-one downdating Wedderburn formula. This formula enables one to better understand the properties of the calculation methods currently available. A number of recently introduced signal-preprocessing methods also fit into the proposed framework. Copyright © 2004 John Wiley & Sons, Ltd. [source] Simultaneous Spectrophotometric Determination of 2-Thiouracil and 2-Mercaptobenzimidazole in Animal Tissue Using Multivariate Calibration Methods: Concerns and Rapid Methods for DetectionJOURNAL OF FOOD SCIENCE, Issue 2 2010Abolghasem Beheshti ABSTRACT:, Two multivariate calibration methods, partial least squares (PLS) and principal component regression (PCR), were applied to the spectrophotometric simultaneous determination of 2-mercaptobenzimidazole (MB) and 2-thiouracil (TU). A genetic algorithm (GA) using partial least squares was successfully utilized as a variable selection method. The concentration model was based on the absorption spectra in the range of 200 to 350 nm for 25 different mixtures of MB and TU. The calibration curve was linear across the concentration range of 1 to 10 ,g mL,1 and 1.5 to 15 ,g mL,1 for MB and TU, respectively. The values of the root mean squares error of prediction (RMSEP) were 0.3984, 0.1066, and 0.0713 for MB and 0.2010, 0.1667, and 0.1115 for TU, which were obtained using PCR, PLS, and GA-PLS, respectively. Finally, the practical applicability of the GA-PLS method was effectively evaluated by the concurrent detection of both analytes in animal tissues. It should also be mentioned that the proposed method is a simple and rapid way that requires no preliminary separation steps and can be used easily for the analysis of these compounds, especially in quality control laboratories. [source] Comparison of traceable calibration methods for primary photovoltaic reference cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2005Harald Müllejans Abstract The calibration of photovoltaic reference cells used as primary laboratory standards for the calibration of photovoltaic devices needs to be traceable to international radiometric standards and SI units. As a contribution to the development of an international standard this paper describes three methods for the calibration of primary photovoltaic reference cells, establishing two independent traceability chains. The solar simulator method is traceable via a standard lamp to the international irradiance scale whereas the global sunlight method and the modified global sunlight method are traceable to the world radiometric reference. The calibration values obtained by the three methods agree with each other within their respective uncertainties and with the world photovoltaic scale within ±,0·8%. Copyright © 2005 John Wiley & Sons, Ltd. [source] A review of forecast error covariance statistics in atmospheric variational data assimilation.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 637 2008I: Characteristics, measurements of forecast error covariances Abstract This article reviews the characteristics of forecast error statistics in meteorological data assimilation from the substantial literature on this subject. It is shown how forecast error statistics appear in the data assimilation problem through the background error covariance matrix, B. The mathematical and physical properties of the covariances are surveyed in relation to a number of leading systems that are in use for operational weather forecasting. Different studies emphasize different aspects of B, and the known ways that B can impact the assimilation are brought together. Treating B practically in data assimilation is problematic. One such problem is in the numerical measurement of B, and five calibration methods are reviewed, including analysis of innovations, analysis of forecast differences and ensemble methods. Another problem is the prohibitive size of B. This needs special treatment in data assimilation, and is covered in a companion article (Part II). Examples are drawn from the literature that show the univariate and multivariate structure of the B -matrix, in terms of variances and correlations, which are interpreted in terms of the properties of the atmosphere. The need for an accurate quantification of forecast error statistics is emphasized. Copyright © 2008 Royal Meteorological Society [source] FTIR microspectroscopy study of composition fluctuations in extruded amylopectin,gelatin blendsBIOPOLYMERS, Issue 4 2001Z. Mousia Abstract The spatial variation in the composition of nonexpanded biopolymer blends prepared by extrusion of mixtures of gelatin with either native or pregelatinized waxy maize starch was studied using a 30-,m aperture FTIR microspectroscopy technique. The ratio of the areas of the "saccharide" bands (953,1180 cm,1) and the amide I and II bands (1483,1750 cm,1) was used to monitor the relative distributions of the two components of the blend. Two calibration methods were used to obtain amylopectin concentration values from the ratios of the IR bands. The results suggested a high degree of heterogeneity in these blends, despite the thorough mixing expected by twin-screw extrusion processing. The concentration fluctuations were greater for the blends produced by extruding gelatin and native waxy maize starch mixtures. This was in agreement with the reduced degree of conversion of the starch granules when extruded in the presence of gelatin. The FTIR 2-dimensional maps obtained suggested that in the blends produced from either native or pregelatinized starch at all concentrations studied (25/75, 50/50, and 75/25 amylopectin/gelatin) the gelatin constituted the continuous phase. The effect of the spatial resolution on the FTIR microspectroscopy results was considered and the proposed interpretation was verified by the use of polarized light microscopy and FTIR microspectroscopy acquired at higher spatial resolution (10 ,m). © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 208,218, 2001 [source] The role of inter-specific, micro-habitat and climatic factors on the carbon isotope (,13C) variability of a modern leaf assemblage from northern Scandinavia: implications for climate reconstructionBOREAS, Issue 2 2006NEIL J. LOADER To provide a basis for the interpretation of past climatic conditions from Quaternary leaf records, leaf carbon isotope (,13C) results are presented for 12 northern European dwarf-shrub, shrub and tree species growing across a network of 18 sites in northern Scandinavia. The role of micro-habitat (hummock/hollow) on carbon isotope trends is explored in addition to a comparison of the carbon isotope composition of both cellulose and wholeleaf material. The data are also examined against local meteorological variables (temperature, precipitation and vapour pressure deficit) at both species and genus levels. Results exhibit only modest coherence between selected plant species and low-order correlations with external climate forcings consistent with accepted models for carbon isotope fractionation. Potential for the analysis and interpretation of stable isotopic time series may still be identified; however, factors such as inter-plant variability, senescence, diagenesis and homogeneity need to be thoroughly addressed before such an approach may be used for palaeoenvironmental reconstructions. These findings highlight the complexities and limitations of spatial calibration methods. [source] | ||||||||||||||||