Methodology for the selection of suitable sensors for incorporation into a gas sensor array

An investigation into suitable mathematical techniques which can be used to select sensor components for a gas sensor array is reported. Data from a tin dioxide Taguchi semiconductor sensor array were obtained individually for various organic solvents and analysed using multivariate techniques, including principal component analysis, cluster analysis and star symbol plots. It was shown that the array data produced a series of characteristic response patterns for the analytes. It was also found that analytes of similar chemical nature had similar response patterns, indicating a correlation between sensor interaction and the chemical functional groups of the analyte. The multivariate techniques used proved to be very useful in enabling a suitable selection of the components of the array to be made by identifying which of the components or sensors were acting independently.     

Harvesting chemical information from the Internet using a distributed approach: ChemXtreme

The Internet is a comprehensive resource of chemical information which is at the same time largely unstructured. It provides a wealth of scientific information such as experimental data and requires a suitable automated data mining and analysis tool for its meaningful exploration. The Java based software presented here, ChemXtreme, is developed for harvesting chemical information from the Internet employing the Google API in combination with a distributed client/server text analysis architecture based on JavaRMI. It represents the first and until now the only toolkit for automated structured data retrieval from the Internet which is itself open source. ChemXtreme employs the "search the search engine" strategy, where the URLs returned from the search engine are analyzed further via textual pattern analysis. This process resembles the manual analysis of the hit list, where relevant data are captured and, by means of human intervention, are mined into a format suitable for further analysis. ChemXtreme on the other hand transforms chemical information automatically into a structured format suitable for storage in databases and further analysis and also provides links to the original information source. The query data retrieved from the search engine by the server is encoded, encrypted, and compressed and then sent to all the participating active clients in the network for parsing. Relevant information identified by the clients on the retrieved Web sites is sent back to the server, verified, and added to the database for data mining and further analysis. The distributed further analysis of URLs in a client/server architecture scales very favorably, thus producing only minimal overhead.     

Multiparametric curve fitting--V: The general program 'ABLET', a system for regression analysis in studies of solution equilibria

The general program ABLET is a system of subprograms for non-linear regression analysis of experimental data to find an appropriate model. The structure of ABLET provides a suitable organizational framework in which just two specific subroutines have to be supplied by the user. The resulting program can estimate non-linear model parameters with their standard deviations, test the agreement between experimental data and a mathematical model, test the accuracy and reliability of the parameters found, and simulate synthetic data for preselected parametric values. Heuristic, and/or algorithmic minimization strategies aid examination of the local and overall minima. The method of construction of the program for a particular system is discussed.     

Treatment of a class-in-class modelling problem in chemical pattern recognition

A supervised learning procedure is described for the detection and characterization of classes which overlap or are located within other classes. The UNEQ classifier proposed by Derde and Massart is extended by applying tests for multivariate homogeneity and homoscedasticity, principal components analysis of each class box, and Boolean-type decision rules. The extended algorithm is suitable for class-in-class modelling. The procedure is applied to chemical data for an environmental problem involving an industrial source of emission and its immission effects.     

The structure of acrolein in a liquid crystal phase

The (1)H NMR spectrum of a sample of acrolein dissolved in the nematic liquid crystal phase I52 has been analysed to yield 18 dipolar couplings between all the magnetic nuclei in the molecule; moreover, the (13)C and (13)C{(1)H} NMR spectra of a sample of acrolein in CDCl(3) were recorded and analysed to determine the indirect J(ij) couplings. The data were used to obtain the relative positions of the carbon and hydrogen atoms, assuming that these are independent of the conformations generated by rotation around the C--C bond through an angle phi, and to obtain a probability distribution P(phi). It has been found that in the liquid phase, the distribution is a maximum at the trans form whereas the abundance of the cis form is significantly smaller compared with that found by microwave spectroscopy or high level quantum mechanical calculations. Such calculations produced also a suitable force field needed to develop suitable strategies for vibrational correction procedure in the case of flexible molecules.     

Computer method for the selection of a suitable stationary phase in gas chromatography

Summary A selection of stationary phases is carried out for a gas chromatographic separation of certain hydrocarbon mixtures with help of a computer. For this purpose a suitable catalogue including the relative retention data of substances investigated on a large number of stationary phases and an algorithm of sequence of operations are proposed. The program written in ALGOL algorithmic language points out three stationary phases being the best for the separation of a certain n-component mixture by the criterion R_{r, k}. Besides the three suitable phases the conditions for a given separation are also pointed out.     

Analysis of temperature programmed desorption (TPD) data for the characterisation of catalysts containing a distribution of adsorption sites

This paper discusses some methods of analysing TPD data for samples obeying first-order desorption kinetics and proposes several improvements to existing practice. The methods apply in the case when the Arrhenius parameters A and E for each site are independent of coverage, and thus are normally suitable for the characterisation of porous solids. An improved implementation of the condensation approximation method is proposed to gain an initial estimate of the adsorption site distribution. Further, a variation of the method is proposed that can be used when A is a function of E. The initial estimate of the distribution can be used to analyse data obtained by an interrupted TPD experiment, in which heating is halted at a specified temperature. This method provides a reliable method of determining the parameter A for a peak in the distribution. Finally, regularisation procedures for obtaining physically sensible distributions from "noisy" TPD data are discussed. It is shown that a penalty function based on the square of the second derivative of the distribution is normally most suitable for analysing TPD data, at least in the case when the L-curve method is used to select the regularisation parameter.     

Automated chromatography in research — a link between laboratory and process analysis

The purpose of pilot plants is to collect data at minimal cost. The analyses required must be cost-effective, fast, flexible and constantly available. Neither central analytical laboratories nor peocess analyzers are suitable for the purpose. The polarization of laboratory analysis and process analysis is discussed and ad-hoc instrumental systems for pilot plants are described. The on-line monitoring equipment is constructed from commercially available instruments or parts for continuous use attended by the plant operator or laboratory staff responsible for optimizing the process. These on-line methods (mainly chromatographic) are based on proven methods of laboratory analysis. Used equipment can be returned to the research laboratory. The recommended mode of action has the advantage that analytical experience is gained as the pilot develops and is ultimately used for the production plant.     

Development of a Tool for Estimation of Pesticide Occurrence in Surface Water Under Danish Conditions

The Danish Environmental Protection Agency initiated in 1998 the development of a modelling tool for estimation of pesticides in surface water in connection with registration of pesticides. The organisations involved in the development are DHI - Water and Environment, National Environmental Research Institute, Danish Institute of Agricultural Science (Flakkebjerg), and the Counties of Funen and Northern Jutland. Two existing small 1st order catchments are chosen as basis for the scenarios. Models are calibrated and validated on existing flow and pesticide data for the two catchments. Finally, the models are modified to create scenarios for registration purposes. The approach differs from the more traditional approach where one field is placed along a stream and the main transport to the stream is expected to take place as drift into a more or less well defined amount of water. Considerable work has gone into the design of a suitable user interface including data input and extraction of data relevant for evaluation of effects.     

Isotope effect of hydrogen bond vibrations in a three-dimensional model

A three-dimensional model is proposed for hydrogen bonds, which may be used to calculate the stretching and bending vibrations of protons and deuterons. The Einstein model for anharmonic oscillators proved suitable for the experimental data of a broad class of crystals. The theoretical results were compared with experimental data. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 6, pp. 343–348, November–December, 1999.     

A method to calculate a global performance index for materials. An application to thermoplastic polymers

More and more frequently, different materials have to be compared to find out the most suitable for a specific use. A large number of individual properties and performances have to be considered at the same time and a synthetic evaluation via a global performance index (GPI) may be very useful. In this paper, a new methodology, previously used for durable goods, is applied for the first time to polymeric materials. The GPI can be obtained, starting from basic parameters expressing the performance of each material considered, through the construction of a ‘relevance tree’ with increasing level of data aggregation. The construction can be performed either graphically or algebraically by using nomograms or a computer implemented algorithm, respectively. In the latter case, the influence of the averaging functions over the final GPI is also discussed.     

Multiresidue procedures for the determination of chlorinated dibenzodioxins and dibenzofurans in a variety of foods using capillary gas chromatography-electron-capture detection

Multiresidue digestion-extraction procedures for the determination of chlorinated dioxins and furans in a wide variety of products are presented. Procedure selection is dependent upon the residue(s) of interest, and on the fat content of the product. Additional cleanup is accomplished using column chromatography and a Florisil trap. The separation of residues is achieved by fraction collection off of two high-performance liquid chromatographic systems. Capillary gas chromatography employing electron-capture detection is used for quantitation. The extracts are suitable for gas chromatography mass spectrometry or gas chromatography with Hall electrolytic conductivity detection. Results of analysis, recovery data, and interlaboratory comparisons are presented. Spike recoveries will typically average 90% +/- 10%.     

Comprehensive time-lag measurement as a diagnostic and analytical tool for non-Fickian transport studies: a salient porous barrier-gaseous permeant test case

Concentration-independent permeation of He, Ne and N2 through a porous barrier, specially constructed by multistep compaction of fine "Carbolac" carbon powder, has been studied. Emphasis was placed on measuring a variety of time lags, supplemented with transient permeation and sorption kinetics. Previous time-lag data, restricted to values of a single time-lag parameter, were instrumental in revealing deviations from Fick's law in similar solid barrier-penetrant systems; however, they could only provide indirect evidence as to the nature of the underlying causes, namely, time- or spatial dependence of the relevant transport parameters. Thus, an interpretation in terms of time-dependence (induced by the presence of blind pores) was proposed, predicated on calculations indicating that, in theory, spatial dependence (induced by non-uniform compaction) could be reduced to insignificance by adoption of a suitable multistep powder compaction technique. The comprehensive time-lag analysis approach applied here is a general diagnostic and analytical tool, previously successfully tested on graphite barriers, that can discriminate rigorously between the aforementioned non-Fickian functional dependences, as well as provide additional substantial information in either case. This capability is well illustrated by the results obtained in the system under study here, which provide unequivocal evidence of substantial spatial dependence. Furthermore, it is shown that the predicted functional form of the detected spatial dependence (i) can, in conjunction with an adequate physical model and with the results of a previous theoretical parametric study, account fully for all aspects of the observed non-Fickian time-lag behaviour and (ii) correlates satisfactorily with variation of local porosity across the barrier, detected by a suitable X-ray imaging technique. On the other hand, there is no evidence, from time lags or transient kinetics, of any significant time-dependence attributable to slow filling or emptying of blind pores or to other causes.     

From data point timelines to a well curated data set, data mining of experimental data and chemical structure data from scientific articles, problems and possible solutions

The scientific literature is important source of experimental and chemical structure data. Very often this data has been harvested into smaller or bigger data collections leaving the data quality and curation issues on shoulders of users. The current research presents a systematic and reproducible workflow for collecting series of data points from scientific literature and assembling a database that is suitable for the purposes of high quality modelling and decision support. The quality assurance aspect of the workflow is concerned with the curation of both chemical structures and associated toxicity values at (1) single data point level and (2) collection of data points level. The assembly of a database employs a novel “timeline” approach. The workflow is implemented as a software solution and its applicability is demonstrated on the example of the Tetrahymena pyriformis acute aquatic toxicity endpoint. A literature collection of 86 primary publications for T. pyriformis was found to contain 2,072 chemical compounds and 2,498 unique toxicity values, which divide into 2,440 numerical and 58 textual values. Every chemical compound was assigned to a preferred toxicity value. Examples for most common chemical and toxicological data curation scenarios are discussed.     

PCGAP: Application to analyze gamma-ray pulse-height spectra on a personal computer under Windows NT®

PCGAP is a software code, which was written to provide gamma-ray pulse height spectrum analysis on a personal computer platform. The code was specifically developed for Windows NT for either an Intel^® or DEC Alpha^® based processor. PCGAP includes programs which can be used to control data collection using a Canberra INSPECTOR^® multichannel pulse-height analyzer. With suitable spectrum conversion routines PCGAP can be used to analyze data from almost any multi-channel analyzer. Besides the normal functions associated with a robust spectrum analysis package, PCGAP can be used for radionuclide analysis for actinides via L-X and gamma-ray spectrometry. It can be used to control and analyze data from an INEEL developed pulse injection system for individual spectrum validation. The package includes programs for the manual analysis of spectra using displays which permit the spectroscopist to interactively define the spectral continuum and peak fitting limits, and display the resulting function fitting forms.     

On-line application of ion chromatography in a thermal power plant

Complete monitoring of the “condensate-feedwater” cycle in power plants requires reliable automatic methods suitable for very low concentrations of various chemical species. A complete on-line ion-chromatography monitoring system is under development. It comprises an automatic on-line sampling system two Dionex Model QUIC (process instrument) ion chromatographs, an on-line calibration systems, and a data acquisition/processing system. The present model serves for the determination of sodium, chloride and sulfate ions. Detection limits are < 1 μg l^?1 (P = 95%) with liner ranges up to 10 μ l^?1 or about 200 μ l^?1 depending on settings. The importance of statistical evaluation of data is emphasized. The instrumentation was tested for sequential samples from crucial points of a 320-MW thermal power station with satisfactory results. Problems of reliability are discussed.     

A numerical method to obtain a symmetry-adapted basis from the hamiltonian or a similar matrix

A practical method is proposed which using the hamiltonian matrix, or some other matrix corresponding to any operator with identical symmetry properties, enables one to obtain the transformation matrix, from the given basis to a symmetry-adapted basis. The method is very suitable for applications in the fields of molecular orbital and force constant calculations.     

Processing and interpretation of core-electron XPS spectra of complex plasma-treated polyethylene-based surfaces using a theoretical peak model

Interpretation of X-ray photoelectron spectroscopy (XPS) spectra of complex material surfaces, such as those obtained after surface plasma treatment of polymers, is confined by the available references. The limited understanding of the chemical surface composition may impact the ability to determine suitable coupling chemistries used for surface decoration or assess surface-related properties like biocompatibility. In this work, XPS is used to investigate the chemical composition of various ultra-high-molecular-weight polyethylene (UHMWPE) surfaces. UHMWPE doped with α-tocopherol or functionalised by active screen plasma nitriding (ASPN) was investigated as a model system. Subsequently, a more complex combined system obtained by ASPN treatment of α-tocopherol doped UHMWPE was investigated. Through ab initio orbital calculations and by employing Koopmans' theorem, the core-electron binding energies (CEBEs) were evaluated for a substantial number of possible chemical functionalities positioned on PE-based model structures. The calculated ΔCEBEs showed to be in reasonable agreement with experimental reference data. The calculated ΔCEBEs were used to develop a material-specific peak model suitable for the interpretation of merged high-resolution C 1 s, N 1 s and O 1 s XPS spectra of PE-based materials. In contrast to conventional peak fitting, the presented approach allowed the distinction of functionality positioning (i.e. centred or end-chain) and evaluation of the long-range effects of the chemical functionalities on the PE carbon backbone. Altogether, a more detailed interpretation of the modified UHMWPE surfaces was achieved whilst reducing the need for manual input and personal bias introduced by the spectral analyst.