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  • 1995-1999  (2,908)
  • 1995  (2,908)
  • Analytical Chemistry and Spectroscopy  (1,554)
  • Engineering  (787)
  • Inorganic Chemistry  (567)
  • Nuclear reactions
Material
Years
  • 1995-1999  (2,908)
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 197-209 
    ISSN: 0886-9383
    Keywords: proficiency test ; true value ; homogeneity robust statistic ; standard ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Profficiency tests raise two types of problems: (i) the homogeneity of a sample must be carefully checked before using it as a reference material; (ii) it is necessary to define a conventional reference value (RV) in order to rank participants. Since these topics are poorly addressed in the literature, a reference material was specially prepared in order to propose a procedure for verifying homogeneity and to establish whether the algorithms classically used to compute the conventional true value have an influence on the conclusion of the test.The homogeneity of the sample was not perfect and univariate and multivariate techniques were used to demonstrate some analytes can be suspected as heterogeneous. However, this was considered adequate for introducing the sample in a large proficiency test organized between four laboratory associations which regularly perform such tests. Altogether more than 3000 measurements were collected and eight algorithms were applied to compute the RV on 14 analytes. Thus is was possible to demonstrate that some of these algorithms are better adapted than others. It is also obvious that some analytes are better suited to proficiency testing.It can be concluded from this work that some effort towards standardization would be profitable to check homogeneity or to compute the RV, especially since the economic weight of proficiency testing is becoming even more important with the development of certification accreditation.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 451-457 
    ISSN: 0886-9383
    Keywords: non-linear regression ; optimization ; robust methods ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several robust regression methods, including a new proposal, are described and their properties discussed. Resistance to various types of outliers and non-normality is demonstrated. The techniques are applied to non-linear regression models from chemical kinetics and calibration. Optimization of the types of objective functions encountered when applying robust regression is considered.
    Additional Material: 5 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 471-481 
    ISSN: 0886-9383
    Keywords: batch prediction ; continuum regression ; multivariate calibration ; sequential prediction ; simultaneous prediction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In analytical chemistry a single fitted calibration model is used repeatedly to predict the level of the analyte of interest for the specimens comprising the prediction set. Unlike the calibration (or training) set, which is often limited in size, the prediction set can be very large.In the case of multivariate calibration a number of methods such as PLS and PCR are commonly used to construct the calibration model. The set of instrumental measurements and the reference analyte level are available for each specimen in the calibration set. For specimens in the prediction set, only the instrumental measurements are available, since the problem is to predict the analyte level for these specimens. It is not widely recognized that predictions of the analyte levels for individual specimens can be improved by utilizing seemingly unrelated information from the instrumental measurements associated with the other members of the prediction set. In the case of PCR there exists a very straightforward procedure for doing this. A description of the various sources of prediction errors is provided to explain the ability of PCR to utilize this additional information. The use of PCR in this context is illustrated with both a synthetic and a real example.
    Additional Material: 1 Ill.
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  • 5
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 21-29 
    ISSN: 0886-9383
    Keywords: Near-infrared absorbance ; Partial least squares ; Principal component regression ; Root-mean-square error of prediction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of principal component regression (PCR) as a multivariate calibration method has been discussed by a number of authors. In most situations principal components are included in the regression model in sequence based on the variances of the components, and the principal components with small variances are rarely used in regression. As pointed out by some authors, a low variance for a component does not necessarily imply that the corresponding component is unimportant, especially when prediction is of primary interest. In this paper we investigate a different version of PCR, correlation principal component regression (CPCR). In CPCR the importance of principal components in terms of predicting the response variable is used as a basis for the inclusion of principal components in the regression model. Two typical examples arising from calibrating near-infrared (NIR) instruments are discussed for the comparison of the two different versions of PCR along with partial least squares (PLS), a commonly used regression approach in NIR analysis. In both examples the three methods show similar optimal prediction ability, but CPCR performs better than standard PCR and PLS in terms of the number of components needed to achieve the optimal prediction ability. Similar results are also seen in other NIR examples.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. i 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 137-138 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0886-9383
    Keywords: pattern recognition ; infrared spectra ; factor analysis ; maximum likelihood method ; entropy of information ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectral region from 700 to 3600 cm-1 is subdivided into several wave number intervals. The peaks in each interval are summarized by means of three encoding algorithms. Using a factor model of kcommon factors, the total extractable variacnce (com) of a given set of intervals is calculated and correlated with the redundancy of information in all these intervals. The value of com is verified by analysis of the factor loadings aik (factor pattern). Finally, the information content of some chosen sets of intervals coded by the three selected feature algorithms will be correlated to the probability of information flow through a serial-parallel network. The encoding using only wave numbers was found to be the most effective.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 211-221 
    ISSN: 0886-9383
    Keywords: diagnostics statistics ; QSAR ; MASCA ; principal component regression ; non-least squares regression ; types of multicollincarity ; flagged observations ; influential points ; high-leverage points ; outliers ; extra-carrier points ; random perturbation ; cluster correalation ; resampling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formal application of a Hansch analysis to a series of 3-quinuclidinyl benzylates (QNBs) led to a ‘statistically significant’ QSAR equation. In contrast, the application of the MASCA model has shown that the design matrix is unsuitable for each QSAR analysis: one sample member is an outlier but not a high-leverage or influential point; another one is an influential point, a high-leverage point and an extra-carrier point. The regressors of the design matrix are multicollinear without predictive model power. The result of such flagged observation and this type of multicollinearity is a multiple cluster correlation. The QNB series is a good example for ‘sampling artifacts’ where no practically important but artificial QSARs can be found.
    Additional Material: 3 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 230-231 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 239-262 
    ISSN: 0886-9383
    Keywords: industrial experimentation ; parameter design ; quality by design ; robust design ; Taguchi method ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this paper is to present a simple structured review of the different approaches to robust process design to clarify their similarities and dissimilarities. It is primarily written for practitioners who wish to understand and compare the main ideas of each approach and to apply them to their work. Two examples are used to illustrate the different approaches and their corresponding data analysis strategies: the first one is a constructed example on a pigment kneading process and the second one is real example dealing with the validation of an HPLC method. A comparison of the different approaches is provided and some practical recommendations are formulated.
    Additional Material: 12 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 323-326 
    ISSN: 0886-9383
    Keywords: partial least squares ; biased regression ; ordinary least squares ; minimum length least squares ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An algebraic proof is given that in partial least squares (PLS) regression the Euclidean length of the estimator is shrunk in comparison with the ordinary least squares estimator or with PLS estimators based on a larger number of dimensions.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 363-372 
    ISSN: 0886-9383
    Keywords: PLS regression ; orthogonal expansion ; optimization ; Lagrange multipliers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple iteration algorithm that is faster and less memory-intensive than the NIPALS iteration algorithm for PLS regression is presented. The iteration algorithm is obtained by treating the orthogonal expansion or decomposition of a matrix X as an extremum problem subject to normalization and orthogonality constraint conditions and then solving the problem by use of the method of Lagrange multipliers. The main idea in this method is to find the transformation vector r. The latent variable t is expressed exactly as the linear combination of X-variables with the vector r so that the final regression coefficients can be conveniently provided. In the algorithm the recursion of the orthogonal projection is needed, which is derived by use of a matrix inverse formula. Algorithms are established from the equation for calculating the vector r that are suitable for dealing with three cases of large data sets. The first case is when the number of objects is very large, the number of variables is relatively small and the number of Y-variables is equal to or greater than the number of X-variables. The second case is when the number of objects is very large, the number of variables is relatively small and the number of X-variables is greater than the number of Y-variables. The last case is when the number of variables, either X- or Y-variables, or both, is very large and the number of objects is small.
    Additional Material: 4 Tab.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 423-430 
    ISSN: 0886-9383
    Keywords: PLS ; neural network ; training ; interpretable ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This communication describes the combination of a feedforward neural network (NN) with one hidden neuron and partial least squares (PLS) regression. Through training of the neural network with an algorithm that is a combination of a modified simplex, PLS and certain numerical restrictions, one gains an NN solution that has several feasible properties: (i) as in PLS the solution is qualitatively interpretable; (ii) it works faster than or comparably with ordinary training algorithms for neural networks; (iii) it contains the linear solution as a limiting case. Another very important aspect of this training algorithm is the fact that outlier detection as in ordinary PLS is possible through loadings, scores and residuals. The algorithm is used on a simple non-linear problem concerning fluorescence spectra of white sugar solutions.
    Additional Material: 4 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 439-439 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 0886-9383
    Keywords: PLS ; kernel algorithm ; multivariate calibration ; EM algorithm ; cross-validation ; missing data ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This is Part II of a series concerning the PLS kernel algorithm for data sets with many variables and few objects. Here the issues of cross-validation and missing data are investigated. Both partial and full crossvalidation are evaluated in terms of predictive residuals and speed and are illustrated on real examples. Two related approaches to the solution of the missing data problem are presented. One is a full EM algorithm and the second a reduced EM algorithm which applies when the number of missing values is small. The two examples are multivariate calibration data sets. The first set consists of UV-visible data measured on mixtures of four metal ions. The second example consists of FT-IR measurements on mixtures consisting of four different organic substances.
    Additional Material: 5 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 509-520 
    ISSN: 0886-9383
    Keywords: canonical variates ; discriminant analysis ; partial least squares ; principal components ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new set of derived variables is proposed for exhibiting group separation in multivariate data on for preprocessing such data prior to discriminant analysis. The technique combines optimal features of canonical variate analysis and principal component analysis: the derived variables are linear combinations of the original variables that optimize the canonical variate criterion (ratio of between-group to within-group variance) but subject to the orthogonality constraints of principal components. In this formulation the canonical variates can be derived even when the within-group matrix is singular (i.e. when there are more variables than objects in the data matrix). A simple computational algorithm for extraction of these variables is proposed. The methods are illustrated on several data sets and compared with alternative techniques such as principal component analysis and partial least squares.
    Additional Material: 7 Ill.
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  • 20
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 22
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 179-195 
    ISSN: 0886-9383
    Keywords: GRAM ; PARAFAC ; rank overlap ; second-order calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GRAM, a method for second-order calibration, has been introduced by Sanchez and Kowalski and later modified by Wilson, Sanchez and Kowalski. The methods are based on the claim that, in cases without measurement error they yield correct estimates for the concentration ratios and profiles of (rank-one) analytes present in sample and mixture. This claim has not been proven rigorously. In the present paper, rigorous proofs are given for situations where the claims are valid indeed. In addition, it is shown that PARAFAC, an alternative method for second-order calibration, can be used to obtain the same results. Next it is shown that the claims do not hold in cases with ‘rank overlap’ (partly overlapping profiles) and it is proven that a procedure by Wang et al. can still be used to assess some of the concentration ratios. A general framework is provided for a variety of second-order calibration problems and the extent to which quantitative and qualitative information can be expected is given.
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  • 23
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 223-225 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 309-322 
    ISSN: 0886-9383
    Keywords: simulated annealing ; messy genetic algorithms ; optimization of multimodal objective functions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The method of simulated annealing is modified so that the concept of messy chromosomes is applied. Constituent genes of messy chromosomes are specified by their respective names (indices) and values (alleles) simultaneously. Unlike simple chromosomes (binary vectors), messy chromosomes may be either under- or overspecified with respect to the problem being solved. The messy simulated annealing algorithm is a very robust and efficient stochastic optimization method which is able to find correct minima of deceptive or highly multimodal objective functions. This is shown by way of a number of simulations.
    Additional Material: 7 Ill.
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  • 25
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. ii 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 26
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 373-387 
    ISSN: 0886-9383
    Keywords: robust regression ; outliers ; spectroscopy ; calibration ; MASBR (maximum sum of binary coded residuals) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, a novel robust regression method, the maximum sum of binary coded residuals (MASBR), is proposed. Instead of the sum of squared residuals used in least squares regression as the minimization criterion, MASBR regression maximizes the sum of binary coded residuals. MASBR regression is designed for cases where the conventional robust regression methods with breakdown points less than 50% fail. To circumvent the problem of being trapped in local optima, a stepwise-varying acceptable error limit (SVAEL) algorithm is proposed. Both numerical simulation and treatment of real analytical data demonstrate the feasibility of MASBR regression in conjunction with the SVAEL algorithm.
    Additional Material: 5 Ill.
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  • 27
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 489-507 
    ISSN: 0886-9383
    Keywords: QSAR ; partial least squares ; robust regression ; CoMFA ; weighted regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A robust implementation of partial least squares (PLS) is developed in which the method of iteratively reweighted least squares is adapted for use with PLS. The result is a PLS algorithm which is robust to outliers and is easy to implement. Examples and case studies are presented, followed by two Monte Carlo studies designed to explore the behavior of the method.The paper begins with the motivation and intended applications for the procedure. A discussion is given of the method of interatively reweighted least squares (IRLS) for outlier detection. The procedure, given the name IRPLS, is then presented. Three case studies illustrate how the procedure works on various types of data and how it should be used. The first Monte Carlo study is designed to determine whether the IRPLS procedure correctly identifies multiple outliers in a wide variety of configurations. The second Monte Carlo study is designed to estimate the breakdown bound of the procedure.
    Additional Material: 6 Ill.
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  • 28
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 31-58 
    ISSN: 0886-9383
    Keywords: Multivariate curve resolution ; Three-way data analysis ; Factor analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new multivariate curve resolution method is presented and tested with data of various levels of complexity. Rotational and intensity ambiguities and the effect of selectivity on resolution are the focus. Analysis of simulated data provides the general guidelines concerning the conditions for uniqueness of a solution for a given problem. Multivariate curve resolution is extended to the analysis of three-way data matrices. The particular case of three-way data where only one of the orders is common between slices is studied in some detail.
    Additional Material: 15 Ill.
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  • 29
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 59-66 
    ISSN: 0886-9383
    Keywords: Mathematical approximation ; Sigmoid curve ; Sensitometric curve ; Photographic material ; Non-linear regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper studies the application possibilities of various mathematical analytical functions to models of approximation of sigmoid sensitometric curves of photographic materials. The newly developed functions have been tested along with approximation functions taken from the literature: the former fulfil the statistical criteria of fitting the regression and experimental curve in the best way. The model functions can be used not only for objective determination of sensitometric quantities but also for determination of the general sensitivity (speed) of photographic materials.
    Additional Material: 2 Ill.
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  • 30
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 31
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 69-89 
    ISSN: 0886-9383
    Keywords: chemometrics ; pattern recognition ; class modeling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different estimators of the Mahalanobis distance (such as that based on the Defrise - Gussenhoven correction) are studied and compared with respect to the bias on the distance and the characteristics (sensitivity and specificity) of the class model.Results obtained using estimators with critical values from χ2-statistics are compared with those obtained using estimators with critical values from β-statistics (training set) and Hotelling statistics (evaluation set).Tables are reported for D-statistics (useful for simulating populations of two categories with selectable theoretical sensitivity and specificity) and for critical values of the Mahalanobis distance obtained from β-statistics.For objects of the training set the estimator of the Mahalanobis distance based on the estimate of the covariance matrix produces models with the optimum sensitivity. The same model has too low a sensitivity for objects of the model category in the evaluation set, but good specificity for objects of outer categories.The estimator with the Defrise-Gussenhoven correction produces enlarged models with too high a sensitivity for objects in the training set, good sensitivity for objects of the model category in the evaluation set and low specificity for objects of outer categories.
    Additional Material: 6 Ill.
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  • 32
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    Journal of Chemometrics 9 (1995), S. 139-141 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 33
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 169-178 
    ISSN: 0886-9383
    Keywords: minimum volume ellipsoid (MVE) estimators ; robust distance method ; pattern recognition ; Hotelling's T2 statistics ; near-infrared spectra ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for pattern recognition analysis of near-infrared spectra has been developed using robust distances determined by minimum volume ellipsoid (MVE) estimators of multivariate location and scatter. Classical methods such as the Mahalanobis distance method often fail in the presence of a moderate number of outliers in a training data set, while robust distance methods can tolerate a considerably larger proportion of outliers in a training data set Outliers can be detected by their relatively large robust distances and can be excluded from a training set without a priori knowledge of the nature of the data set. In this paper the properties of a robust distance method are examined using near-infrared spectra of sulfamethoxazole and mixtures with its major degradation products, sulfanilic acid and sulfanilamide. The robust distance method successfully detected unacceptable samples (71.4%-89.3% (α = 0.05) or 78.6%-92.9% (α = 0.10)) even when they were inadvertently included in the training data set.
    Additional Material: 3 Ill.
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  • 34
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    Journal of Chemometrics 9 (1995), S. 226-228 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 35
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    Journal of Chemometrics 9 (1995), S. 229-229 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 36
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    Journal of Chemometrics 9 (1995), S. 283-308 
    ISSN: 0886-9383
    Keywords: simulated annealing ; threshold acceptance ; wavelength selection ; selectivity ; optimization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simulated annealing (SA) is a stochastic search method that has been applied to combinatorial search problems in chemometrics. Unlike strict iterative improvement methods, SA tolerates temporary moves to detrimental parameter configurations during an optimization. The method used by SA to decide whether or not to accept detrimental steps is a special case of a more general acceptance rule. The present work investigates the performance of various SA-type algorithms that differ only in the acceptance rule for detrimental steps when optimizing continuous or discrete problems. A method for step width modulation is introduced to overcome the poor ability of SA type algorithms to locate the exact extreme of a function. The studied search strategies are modified for the discrete problem of wavelength selection. In order to evaluate SA-type algorithms and their abilities to deal with the wavelength selection problem, two global measures of selectivity are used as criteria to determine the most suitable wavelength subset that maximizes selectivity for pure component ultraviolet-visible spectra.
    Additional Material: 7 Ill.
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  • 37
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    Journal of Chemometrics 9 (1995), S. 329-330 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 38
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    Journal of Chemometrics 9 (1995), S. 331-342 
    ISSN: 0886-9383
    Keywords: partial least squares (PLS) ; variable selection ; IVS-PLS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the aim of developing PLS models with improved predictive properties, an interactive variable selection (IVS) approach for PLS regression was introduced in Part I of this series. IVS-PLS is based on a dimension-wise selective removal of single elements in the PLS weight vector w. IVS uses cross-validation (CV) as a guiding tool. The present paper illustrates the use of IVS-PLS on both simulated data and real examples from chemistry. In the first example, spectrophotometric data were simulated according to an experimental design. The objective was to see how IVS-PLS was influenced by different levels of noise in X and Y and by the number of predictor variables (K). The results of the modelling are shown as response surfaces. In addition, four real examples were modelled by the IVS-PLS technique. The real data sets were chosen to reflect different types of data from chemistry. For each example a comparison of ‘prediction error sum of squares’ (PRESS) between IVS-PLS and classical PLS is madeFor most of the examples containing many predictor variables IVS-PLS shows an improvement in predictive properties over classical PLS. Also, improvements for IVS-PLS2 (modelling of more than one y-variable) models were found. For data sets with a moderate number of variables the influence of the IVS method becomes less pronounced.
    Additional Material: 3 Ill.
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  • 39
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    Journal of Chemometrics 9 (1995), S. 389-409 
    ISSN: 0886-9383
    Keywords: multivariate image analysis ; principal component analysis ; exploratory data analysis ; projection in multivariate space ; graphical visualization ; noise ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multivariate image analysis (MIA) is a powerful tool for many image segmentation and classification problems, but the interpretation and understanding of the original and resulting multidimensional (multivariate) data are not always easy. A strategy for MIA has been proposed which describes its usage on multivariate images for segmentation tasks. MIA starts with principal component analysis (PCA) and then continues with interactive analysis of the output from PCA. In this paper a number of extensions to MIA are proposed. The extensions are the suggestion to incorporate preprocessing of the multivariate image in MIA, the suggestion to use synthetic multivariate image models which create a clear-cut situation, and new visualization tools which improve the interactivity and understanding of the results. Extended MIA is applied on synthetic multivariate image data simulating a possible application with large noise, positron emission tomography (PET). As a result of the interactive analysis, suggestions for preprocessing emerge. The developed methodology for handling the noise is then applied on real PET image data with good results.
    Additional Material: 20 Ill.
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  • 40
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 41
    ISSN: 0886-9383
    Keywords: sequential response surface modelling ; Williamson ether synthesis ; SN2 ; optimization ; reaction kinetics ; reaction mechanism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work the utility of a new method for determining kinetic parameters by sequential response surface modelling, previously described (Part 1), is shown by applying it to an experimental study of a reaction with known kinetics. The nucleophilic substitution reaction between ethoxide and benzyl chloride, the Williamson ether synthesis, was selected as a model reaction. This reaction is known to proceed with second-order kinetics. The method gives access to estimates of initial reaction rate which can be further used to obtain estimates of activation energy and reaction order of reactants. The results obtained are in good agreement with the estimated values of these parameters obtained with conventional kinetic experiments.
    Additional Material: 2 Ill.
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  • 42
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    Journal of Chemometrics 9 (1995), S. 483-487 
    ISSN: 0886-9383
    Keywords: fractional factorial design ; multiresponse ; PLS ; PCA ; reduced-rank regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents an interpretation of PLS applied to orthogonal explanatory variables. In particular, it is shown that in fractional factorial multiresponse experiments PLS2 gives identical results to ordinary least squares applied to principal components of the response variables. The general relationship is that the reduced-rank regression algorithm which first projects Y onto the X-space and then truncates this matrix by principal component analysis before performing ordinary least squares estimation gives the same predictor as PLS2 and SIMPLS if all the non-zero eigenvalues of XTX are identical.
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  • 43
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 44
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 45
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    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 46
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    Journal of Chemometrics 9 (1995), S. 1-2 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 47
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    Journal of Chemometrics 9 (1995), S. 3-20 
    ISSN: 0886-9383
    Keywords: Deconvolution algorithms ; Instrumental analysis ; Spectrometry ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deconvolution algorithms for measurand reconstruction are considered. Their metrological and numerical properties are briefly characterized. Six algorithms most frequently used for instrumental applications are selected for closer analysis. Their comparative study is based on the use of spectrometric-type synthetic data, calorimetric-type synthetic data and spectrometric real-world data. Conclusions concerning computational complexity and accuracy of the compared algorithms as well as their metrological applicability are drawn.
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  • 48
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    Journal of Chemometrics 9 (1995), S. 67-68 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 49
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    Journal of Chemometrics 9 (1995), S. 125-135 
    ISSN: 0886-9383
    Keywords: Procrustean analysis ; FT-IR spectroscopy ; NIR spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Procrustean methods allow the fitting of a given matrix to another given matrix observed on the same objects. In the traditional approach orthogonal constraints are imposed upon the transformation matrix, whereas in the alternative approach Procrustean analysis may be performed without such constraints. The two methods (with and without constraints) were compared on data dealing with mid- and near-infrared spectra of oil. The aim was to reconstruct the mid-infrared spectral information using data from the near-infrared spectra. Unconstrained Procrustean analysis proved to be the more efficient for both the calibration and verification sets. Furthermore, the analysis of the transformation matrix between the two infrared ranges made it possible to indicate wavelengths and wave numbers corresponding to the same chemical groups.
    Additional Material: 7 Ill.
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  • 50
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    Journal of Chemometrics 9 (1995), S. 91-123 
    ISSN: 0886-9383
    Keywords: H-principle ; PCA ; PLS regression ; latent variable models ; quadratic models ; sensitivity analysis ; outlier tests ; prediction variances ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present here an algorithmic approach to modelling data that includes principal component analysis (PCA) and partial least squares (PLS). In fact, the numerical algorithm presented can carry out PCA or PLS. The algorithm for linear analysis and extensions to non-linear analysis applies to both PCA and PLS. The algorithm allows for combination of PCA and PLS types of models and therefore extends modelling to new types of models that involve combination of regression models and ‘selection of variation’ models, which is the idea of PCA-type models. The fact that the algorithm carries out both PCA and PLS shows that PCA and PLS are based on the same theory. This theory is based on the H-principle of mathematical modelling. The algorithm allows tests for outliers, sensitivity analysis and tests of submodels. These aspects of the algorithm are treated in detail. We compute various measures of sizes, e.g. of components, of the covariance matrix, of its inverse, etc. that show how much the algorithm has selected at each step. The analysis is illustrated by data from practice.
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  • 51
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    Journal of Chemometrics 9 (1995), S. 232-236 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 52
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    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 53
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 54
    ISSN: 0886-9383
    Keywords: multiway data ; standard addition method ; calibration ; matrix effects ; trilinear decomposition ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Presented here is an algorithm for analysis of second order data by the method of standard additions. The method of standard additions is applicable when matrix effects make traditional calibration unreliable. The algorithm employs a generalized eigenproblem to mathematically separate the instrument response of the analyte from the instrument response of any interfering species. A scheme for determining the eigenvectors (and hence the concentration estimate) that uniquely correspond to the analyte of interest is given. These eigenvectors can readily be distinguished from any eigenvector that corresponds to the spectrum of the interferents or both the interferents and analyte. The stability of the estimated analyte concentration is verified by Monte Carlo simulations. The algorithm is applied to the analysis of trichloroethylene in samples that have matrix effects caused by an interaction with chloroform.
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  • 55
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    Journal of Chemometrics 9 (1995), S. 327-328 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 56
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    Journal of Chemometrics 9 (1995), S. 343-362 
    ISSN: 0886-9383
    Keywords: straight line calibration ; errors in both axes ; uncertainties ; linear regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calibration is a fundamental step in the calculation of the unknown concentration of analyte in most analytical methods. It is known that for certain methodologies, if only the errors in the independent variable are taken into account, there may be considerable errors in the estimation of the value of the regression coefficients, the derived statistical parameters and in some cases the sought for response and concentration values. This paper reviews the calibration methods including some references to procedures for the detection of outliers and robust regression when there are errors in both axes. The advantages and limitations of the different approaches are discussed and a comparative study is made of the approaches of several techniques for which computer programmes have been developed based on the algorithms put forward by the different authors. Finally, some trends of future development in this field are envisaged.
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  • 57
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    Journal of Chemometrics 9 (1995), S. 411-422 
    ISSN: 0886-9383
    Keywords: gasoline ; classification ; multiple regression ; non-correlated variables ; accuracy of measurements ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure for the classification of motor gasolines by their trend to carburettor icing has been proposed. For this goal a set of regression models was employed. Motor gasoline classification was carried out in terms of the isopropyl equivalent using seven physicochemical properties.
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  • 58
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    Journal of Chemometrics 9 (1995), S. 431-432 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 59
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 60
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    Journal of Chemometrics 9 (1995), S. 531-531 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 61
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 74-74 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 62
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 77-94 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A two-dimensional lossy shunt TLM node is incorporated into a TLM system and adapted to model for the first time the Maxwell field equations in thin semiconductor samples. Both the characteristics of the node and the TLM system itself are fully described. By considering a parallel-plate structure containing a thin GaAs sample, driven by a voltage source, it is shown, with an example, that this TLM technique can simulate the response of non-stationary electromagnetic fields in a semiconductor to applied excitations.
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  • 63
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 149-149 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 64
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 315-330 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Transmission-line laser models (TLLMs) are time-domain models suitable for the simulation of complex phenomena in semiconductor lasers. TLLMs include time-domain filters based on transmission-line stubs to model the spectral dependence of the material gain. In this paper, numerical simulations are presented which show that the accuracy of these gain models is dependent on the model's iteration timestep. Analytical formulae are derived that relate the accuracy of the filters to the timestep, filter centre frequency, and filter bandwindth. A new wideband stub filter which allows the material gain to be modelled using a larger timestep is presented. This is equivalent to a digital infinite-impulse-response filter, which is more computationally efficient than finite-impulse-response filters, and is unconditionally stable. The new gain model can improve the computational speed for simulating for multimode Fabry-Perot lasers by a factor of 10-100.
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  • 65
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 383-383 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 66
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 67
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 221-232 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a parallel three-dimensional finite difference time-domain (FDTD) code for electromagnetic field simulation that has been developed for the Connection Machine (CM-2). The CM-2 is briefly discussed. Then the FDTD method is reviewed using a one-dimensional example, and the extensions required for the 3-D case are outlined. The parallelization of the FDTD method is considered, and a simple analytical timing model is dervied. This model predicts the efficiency of the parallelized algorithm as a function of grain size. Some specific points relating to the implementation of the parallel FDTD algorithm in Fortrans-90 on the CM-2 are discussed. Timing data for the parallel 3-D FDTD code measured on a CM-2 is presented and compared qualitatively with the theoretical model. These results are then put into perspective for a particular computations electromagnetics problem, viz. the development of software tools for full-wave modelling of 3-D optical devices. Finally, we draw some conclusions about this work.
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  • 68
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 455-455 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 69
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 447-454 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A novel procedure for synthesizing multilayered radar absorbing materials (RAMs) is presented. The procedure uses a method for global minimization of multimodal functions of continuous variables based on simulated annealing (SA). The technique is very flexible and reliable, allowing the design of absorbing materials for any grazing or normal angles over the specified frequency bandwidth. The technique is particularly suitable for the efficient design of broadband RAMs and hence for EMC applications.
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  • 70
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 187-203 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This document describes the background and motivation behind the PEPSE project. It describes separately the components which make up PEPSE, the parallel design philosophy and aspects of parallel implementation.
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  • 71
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 382-383 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 72
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 417-429 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The scattering of conducting regular polyhedrons of resonant size is studied by means of the electrical field integral equation (EFIE) and the method of moments (MoM). Two models are generated for each polyhedron, a wire grid model and a triangular patch model. Two numerical codes associated with those modelling techniques are used to obtain the radar cross section (RCS) of the polyhedrons. The calculated results are compared with the analytical results of the scattering of a perfectly conducting sphere. Practical criteria relating geometric properties of the sphere and the polyhedrons are investigated for the modelling of curved surfaces by facets in electromagnetic simulations.
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  • 73
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 431-445 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The paper presents the application of nonlinear neural optimization networks to solve the linear complementarity problem. Two different approaches are presented and investigated: one leading to linear and the second to quadratic optimization programming. The numerical results of illustrative examples are given and discussed.
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  • 74
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 75
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    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 3-12 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper details the use of a circuit-based EM modelling technique combined with a harmonic balance simulator used to model the radiation from the microstrip bodies comprising an active antenna circuit. The modelling approach adopted for the planar bodies in the circuit will be shown to allow the use of concurrent algorithms in order to reduce overall computational time.
    Additional Material: 8 Ill.
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  • 76
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 13-27 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents an analysis of the numerical algorithms used to model microwave semiconductor devices. A comparison is made of the relative merits and features of the more popular finite difference schemes. A new generalized Scharfetter-Gummel formulation is presented which is compatible with drift diffusion and energy-transport formulations, and is suitable for implementing in two-dimensional simulations on personal computers. The treatment allows for fully degenerate semiconductors, but implementation for the nondegenerate situation is easily obtained as a special case. The convergence and stability properties of the generalized scheme are discussed. The simulation of a planar submicrometre gate length GaAs MESFET is used to illustrate the application of these algorithms.
    Additional Material: 4 Ill.
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  • 77
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 367-379 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The behaviours of parasitic bipolar transistors are investigated by exploring the physical mechanisms of negative resistance characteristics generated in a small-sized MOSFET structure. Physical experiments and three-dimensional simulations verify the expected negative resistance characteristics. The effects of variations of device parameters such as injected substrate current levels, doping concentrations, channel widths, and physical device sizes are investigated by simulation. According to simulation results, the operation of a parasitic bipolar transistor is initiated by the injected substrate current; this explains the negative resistance characteristics occurring at low operating voltages.
    Additional Material: 13 Ill.
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  • 78
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 243-248 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Two separate exercises on a similar theme are reported. In the first, the moment-method program NEC was extensively modified in order to optimize its performance on a four-processor Cray X-MP computer. In the second exercise, the MININEC moment-method program was completely rewritten into the occam programming language so that it could be executed directly by a transputer system. The NEC exercise exploited judicious use of vectorization and alternative parallelization techniques and achieved a reduction of run times by factors of about five or more. The MININEC exercise has so far achieved only a modest reduction in run-time but it has the potential for a much greater improvement if an optimum strategy for configuring the transputer network is implemented.
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  • 79
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 277-281 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A parallel implementation of the finite difference time-domain algorithm for the analysis of planar microwave circuits is presented in this paper. For this the FDTD mesh is divided in equal-sized subspaces. Every processor of the parallel computer calculates the field in one subspace. Furthermore detailed efficiency investigations are made to predict the timing performance of the parallel FDTD simulator.
    Additional Material: 5 Ill.
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  • 80
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 293-299 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper a parallel algorithm is created for solving electromagnetic wave scattering problems. The algorithm based on the finite difference time-domain (FDTD) representation of the Maxwell's equations written in 3L Parallel Fortran for use on a transputer array.The problem simulated consists of a space (air) where a spherical dielectric scatterer is located. This space is subdivided into fine equisize meshes extending throughout the 3-D domain; the excitation wave is of sinusoidal form. Geometric decomposition is used as the principal algorithm strategy.Results are presented for the performance of the classical sequential algorithm and compared with the parallel algorithm in terms of computational speed-up.
    Additional Material: 6 Ill.
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  • 81
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 385-398 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A typical application of numerical frequency-domain computations is the calculation of electromagnetic fields in cavities. Not only the field vectors of the desired modes, but also parameters such as the resonance frequency and, in the lossy case, the damping coefficient and the quality factor of the cavity can be obtained. This problem leads to an analytical eigenvalue equation, which can be transformed in an algebraic, complex, linear eigenvalue problem by the finite integration method.The consideration of energy losses in materials is straighforward in the analytical theory, using complex material quantities, but it is still a difficult subject area to solve a complex algebraic eigenvalue problem. Generally problems with very large, complex matrices (dimension 〉100,000) have to be solved, and no commonly applicable algorithm is known so far.This paper deals with a special variant of subspace iteration with polynomial acceleration, and some problems of the application of the complex Chebyshev polynomials are discussed. Two examples with weakly lossy cavities demonstrate the capability of the new algorithm, which is successfully applied to very large problems of up to 490, 000 real unknowns.
    Additional Material: 9 Ill.
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  • 82
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 265-275 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Parallel algorithms for the finite difference time-domain (FDTD), the planar generalized Yee (PGY), and the finite element time-domain (FETD) methods are presented. The FDTD and the PGY algorithms are both explicit time-domain solutions of Maxwell's equations, while the PGY algorithm is based on an unstructured grid. The FETD algorithm is a semi-implicit solution of Maxwell's equations using variational principles, and thus requires a matrix inversion for every time iteration. The three parallel algorithms are based on spatial decompositions of the discrete three-dimensional problem spaces. A comparative analysis of the parallel algorithms is presented based on their memory and computational efficiency as well as their parallel efficiency.
    Additional Material: 1 Ill.
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  • 83
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 313-313 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 84
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 381-381 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 85
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 399-416 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A non-stationary longitudinal model of a thermal two-component plasma is investigated with numerical methods based on so-called high-resolution schemes. The inhomogeneous model system is solved numerically applying a splitting method, where the homogeneous conservation laws for the electrons and ions are approximated by explicit Godunov-type schemes. Coupling of both plasma components is achieved by the electric field, which is also calculated in an explicit manner after reformulating Coulomb's law. A new numerical method is proposed for the expansion of the plasma into the vacuum. This tracking method is based on the solution of the vacuum Riemann problem and avoids the difficulties of numerical approximation introduced by the vacuum where the longitudinal plasma model is not valid. This new approach of tracking resolves sharply the plasma vacuum interface and captures this boundary very well during the temporal evolution of the model system. Two test problems show the interplay, the quality and properties of the approximation methods applied.
    Additional Material: 8 Ill.
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  • 86
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 87
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 153-168 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In electromagnetics, a numerical technique that finds immense application is the method of moments. This method reduces the boundary value problem containing integro-differential equations into the form AX = Y, where A is a full complex matrix, that is known and X is the unknown to be solved for the given excitation Y. In this paper, the matrix equation has been solved on various computers such as the VAX 3500, VAX 8530, Multimax 320, Alliant FX/80 and IBM 3090-600E. Two of the established methods, viz. gaussian elimination and the conjugate gradient method have been used to solve the above matrix equations. A detailed timing analysis has been done to bring out the features of various computer architectures.
    Additional Material: 4 Ill.
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  • 88
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 233-242 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper examines the use of parallel processing techniques for the electromagnetic field analysis of multilayered microwave interconnects. These techniques are applied to a full-wave formulation using an integral equation approach in the frequency domain. In order to demonstrate the feasibility of parallelization and to assess its performance advantages, several variations of the computer code have been developed. Performance tests using domain partitioning and load balancing were conducted on a 32-processor shared-memory machine (KSR1).
    Additional Material: 9 Ill.
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  • 89
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 249-263 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The planar generalized Yee (PGY) algorithm is an extension of the generalized Yee algorithm and the discrete surface integral (DSI) methods, which are based on explicit time-marching solutions of Maxwell's equations. Specifically, the PGY algorithm exploits the planar symmetries of printed microwave circuit devices, achieving great savings in both CPU time and memory. Since the PGY algorithm is an explicit method, it has a high degree of parallelism. To this end, a highly scalable parallel algorithm based on a spatial decomposition of the general unstructured mesh is presented. Two spatial decompositions are compared, the recursive inertia partitioning (RIP) algorithm and the Greedy algorithm. The Greedy algorithm provides optimal load balance, whereas the RIP algorithm more effectively minimizes shared boundary interface lengths. Through numerical examples, It is demostrated that the Greedy algorithm provides superior speedups. It is also demonstrated that the parallel PGY algorithm is a highly scalable algorithm.
    Additional Material: 11 Ill.
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  • 90
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 283-291 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The finite difference time-domain (FDTD) method is a well known numerical technique that has been used to solve electromagnetic boundary value problems. However, the method requires large computational resources to solve a problem, restricting its use on sequential computers to small problems.This has led to the use of expensive supercomputers in the past to solve larger problems. In this paper we first discuss existing parallel implementations of the FDTD method. We then describe an approach to compute the FDTD equations based on distributed- memory computer architectures. Finally we evaluate a low-cost parallel implementation of the FDTD method that runs on a network of Workstations, utilizing spare network capacity.
    Additional Material: 6 Ill.
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  • 91
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 301-312 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: In this paper, the potential use of cellular automata machines for electromagnetic field solution is investigated. Cellular automata are computational models that operate on a discrete spatial lattice, evolve in discrete time, and employ simple discrete variables. We specifically examine the lattice gas automata which use simple variables to describe particles that interact with nearest neighbours on the lattice through simple rules. They are suitable for modelling the linear wave equation in two dimensions. A benefit of the cellular automata approach is that low-cost, special-purpose digital hardware exists for their efficient evaluation. The current state-of-the-art cellular automata machine is CAM-8. Computational experiments carried out on CAM-8 are provided for problems involving plane wave interaction with perfectly conducting and dielectric media in two dimensions. The examples indicate the potential use of lattice gas automata for modelling electromagnetics and their efficient evaluation using cellular automata machines.
    Additional Material: 7 Ill.
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  • 92
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 73-73 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 93
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 94
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 109-125 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes a computer program for generating finite element meshes for electron guns. Two new methods, the ‘projection’ and the ‘mesh density function’ methods, are used to generate the mesh. The new methods enable the mesh distribution to be set smothly and changed easily, and also enable the mesh distribution to be adjusted according to parameters associated with the gun configuration or by feedback from the electric field calculation. The new program, which can handle a large variety of complicated electron gun structures, has been used in conjunction with the SOGUN program which has been developed by Zhu and Munro for electron gun simulation.
    Additional Material: 14 Ill.
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  • 95
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995) 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 96
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 341-356 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A novel transmission-line model for the minority carrier transport through quasi-neutral arbitrarily doped layers is proposed. Based on detailed drift-diffusion equations, the novel TLEC includes the inductance that represents the influence of the relaxation-time term. Coupled with a object-orientated hybrid circuit simulator, the novel transmission-line model is implemented for the transient analysis of minority carrier transport. A substantial longer storage time of the minority carrier transient current at the collector end of ultra-narrow base is predicted owing to inclusion of the relaxation-time term.
    Additional Material: 10 Ill.
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  • 97
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 151-151 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 98
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 169-185 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes the implementation of transmission-line matirix (TLM) method algorithms on a massively parallel computer (DECmpp 12000), the technique of distributed computing in the UNIX environment, and the combination of TLM analysis with Prony's method as well as with autoregressive moving average (ARMA) digital signal processing for electromagnetic field modelling. By combining these advanced computation techniques, typical electromagnetic field modelling of microwave structures by TLM analysis can be accelerated by a few orders of magnitude.
    Additional Material: 10 Ill.
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  • 99
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 205-219 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: PMC-3D, a parallel three-dimensional (3-D) Monte Carlo device simulator for multicomputers is discussed. The parallel algorithm is and extension of the standard Monte Carlo device simulation model in three dimensions, that combines the stockastic Monte Carlo particle simulation method with a solution of Poisson equation for quasi-static problems, and full Maxwell's equations for microwave or electro-optic phenomena. While our implementation of the Poisson solver is based on an iterative method that uses and odd/even ordering with Chebyshev acceleration, a simple leapfrog method based upon the computational unit of Yee cell is used in a finite-difference, time-domain (FDTD) formulation to solve Maxwell's equations.The parallel algorithms were implemented on a 1024-node distributed memory nCUBE multicomputer. In this work, we present the application of PMC-3D to generate the static current-Voltage characteristics of GaAs MESFET, and to simulate photogenerated femtosecond electrical transients produced in coplanar stripline on a GaAs substrate.
    Additional Material: 10 Ill.
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  • 100
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 51-60 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Simulators in power electronics are less developed than in other electronic fields. The main modelling methods are between the numerical simulation of semiconductor device equations that hardly simulate circuits, and equivalent circuit models that show poor accuracy. We propose the application of the bond graph techniques to model modular power semiconductor devices. Furthermore, the IGBT is a new power device which combines a bipolar transistor with a MOSFET transistor. We develop a new IGBT bond graph model. The bond graph techniques give us good primary simulation results. We present in this paper the principle and the results of this modelling method.
    Additional Material: 16 Ill.
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