Maximum margin Bayesian network classifiers

We present a maximum margin parameter learning algorithm for Bayesian network classifiers using a conjugate gradient (CG) method for optimization. In contrast to previous approaches, we maintain the normalization constraints on the parameters of the Bayesian network during optimization, i.e., the probabilistic interpretation of the model is not lost. This enables us to handle missing features in discriminatively optimized Bayesian networks. In experiments, we compare the classification performance of maximum margin parameter learning to conditional likelihood and maximum likelihood learning approaches. Discriminative parameter learning significantly outperforms generative maximum likelihood estimation for naive Bayes and tree augmented naive Bayes structures on all considered data sets. Furthermore, maximizing the margin dominates the conditional likelihood approach in terms of classification performance in most cases. We provide results for a recently proposed maximum margin optimization approach based on convex relaxation. While the classification results are highly similar, our CG-based optimization is computationally up to orders of magnitude faster. Margin-optimized Bayesian network classifiers achieve classification performance comparable to support vector machines (SVMs) using fewer parameters. Moreover, we show that unanticipated missing feature values during classification can be easily processed by discriminatively optimized Bayesian network classifiers, a case where discriminative classifiers usually require mechanisms to complete unknown feature values in the data first.     

Measurement technique for the thermal properties of thin-film diaphragms embedded in calorimetric flow sensors

In diaphragm-based micromachined calorimetric flow sensors, convective heat transfer through the test fluid competes with the spurious heat shunt induced by the thin-film diaphragm where heating and temperature sensing elements are embedded. Consequently, accurate knowledge of thermal conductivity, thermal diffusivity, and emissivity of the diaphragm is mandatory for design, simulation, optimization, and characterization of such devices. However, these parameters can differ considerably from those stated for bulk material and they typically depend on the production process. We developed a novel technique to extract the thermal thin-film properties directly from measurements carried out on calorimetric flow sensors. Here, the heat transfer frequency response from the heater to the spatially separated temperature sensors is measured and compared to a theoretically obtained relationship arising from an extensive two-dimensional analytical model. The model covers the heat generation by the resistive heater, the heat conduction within the diaphragm, the radiation loss at the diaphragm’s surface, and the heat sink caused by the supporting silicon frame. This contribution summarizes the analytical heat transfer analysis in the microstructure and its verification by a computer numerical model, the measurement setup, and the associated thermal parameter extraction procedure. Furthermore, we report on measurement results for the thermal conductivity, thermal diffusivity, and effective emissivity obtained from calorimetric flow sensor specimens featuring dielectric thin-film diaphragms made of plasma enhanced chemical vapor deposition silicon nitride.     

Trichloroacetic acid‐imprinted polypyrrole film and its property in piezoelectric quartz crystal microbalance and electrochemical sensors to application for determination of haloacetic acids disinfection by‐product in drinking water

A molecularly trichloroacetic acid (TCAA) imprinted non‐crosslinked polypyrole (TCAA‐MIPpy) has been successfully prepared and evaluated in its properties for both piezoelectric quartz crystal microbalance (QCM) and electrochemical means of detection, and application of such sensors for determination of haloacetic acid concentrations in water. Haloacetic acid selectivity was demonstrated in gravimetric or in electrochemical sensors via either cyclic voltammetric or inter‐digitated conductometric (IDC) analyses studies upon comparison with nonimprinted polypyrrole and TCAA‐imprinted polypyrrole. The measurement results with all these systems revealed that the prepared molecularly imprinted polymer can recognize TCAA well from structurally similar compounds. The TCAA‐MIPpy incorporated with only the IDC transduction system produced the specific signal for TCAA detection in aqueous environment, which is useful for the quantifying TCAA disinfection by‐product in water. The analytical application for determination of TCAA in real‐life samples was readily achieved with the incorporation of TCAA‐MIPpy in the IDC analysis system, the results revealing the high sensitivity and selectivity of the method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A Study on the Buckling Behaviour of Strips and Plates with Residual Stresses

During and after rolling or flattening of metal strips and plates the permissible deviations from flatness are described by the permissible absolute wave height and the flatness index. Both values can be determined on a measuring table while the material is not subjected to global tension. Because this procedure is expensive, time‐consuming and allows measurement only at discrete positions along the strip length, on‐line flatness measuring systems are used which can detect the distribution of longitudinal tensile stresses distributed across the strip width allowing for the calculation of the flatness index. This value does not always agree with the value obtained directly by measuring on the table even when the measurement of the longitudinal tensile stress distribution operates perfectly. It can be shown that the measurement of the tensile stress distribution does not give a direct indication on the wave height in the tension‐free state determined on the measuring table. To explain the relationship between tensile stress distribution in the strip and the flatness measurement on the measuring table, the buckling behavior is analysed both with and without dead load for simple symmetrical residual stress distributions resulting, e.g., from the rolling process. Based on the knowledge of the distribution of the longitudinal residual stresses across the strip width, the flatness index and the wave height can be determined by using a specialized finite element model. If the direct measurement is performed under action of dead load, large differences between the directly and indirectly obtained flatness index are observed. Below a certain limit of the intensity of the residual stress distribution the strips and plates lie flat on the measuring table. Above this limit the strip lying on the table exhibits post‐bucking deformations. In the latter case, the wave height increases with strip thickness and intensity of residual stresses.     

Dynamic linking of software components

Traditionally, dynamic linkers merely combined previously compiled pieces of code. Faster processors are now making outright code generation at load time practical, leading to cross-platform portability at very little extra cost. While the central idea behind dynamic linking is quite straightforward, it can be implemented through a surprising variety of strategies. The author contrasts three simple dynamic linking schemes with two much more elaborate strategies. The latter represent a workload shift from the compiler to the dynamic linker, just as dynamic linking itself represents a shift that moves the functions of a separate linker into the loader. Because the new techniques promise the profound additional benefit of cross-platform portability, they will most likely displace the currently popular linking-loader approach     

Cloning of the bile salt hydrolase (bsh) gene from Enterococcus faecium FAIR-E 345 and chromosomal location of bsh genes in food enterococci

Enterococcus faecium strain FAIR-E 345 isolated from food was shown to possess bile salt hydrolase (Bsh) activity in a plate screening assay and by high-performance liquid chromatography analysis. The bsh gene was cloned and sequenced. DNA sequence analysis revealed that it encoded a protein of 324 amino acids, with pI 4.877. A bsh gene probe was prepared from the cloned bsh gene and was used for probing plasmid and total genomic DNA of Bsh-positive enterococci isolated from food to determine the genomic location of their bsh genes. This probe was able to detect the bsh gene among total genomic DNA preparations but not from plasmid preparations of 10 plasmid-bearing Enterococcus strains. However, the probe could detect the bsh gene from total genomic DNA preparations of 12 Enterococcus strains that did not contain detectable plasmid DNA. In no cases did the probe hybridize with plasmid DNA preparations, suggesting that the bsh gene among enterococci is probably generally chromosomally encoded. This presumptive chromosomal location of bsh genes among food enterococci suggests that transfer of this trait by conjugative plasmids is unlikely.     

Enterococci as probiotics and their implications in food safety

Enterococci belong to the lactic acid bacteria (LAB) and they are of importance in foods due to their involvement in food spoilage and fermentations, as well as their utilisation as probiotics in humans and slaughter animals. However, they are also important nosocomial pathogens that cause bacteraemia, endocarditis and other infections. Some strains are resistant to many antibiotics and possess virulence factors such as adhesins, invasins, pili and haemolysin. The role of enterococci in disease has raised questions on their safety for use in foods or as probiotics. Studies on the incidence of virulence traits among enterococcal strains isolated from food showed that some can harbour virulence traits, but it is also thought that virulence is not the result of the presence of specific virulence determinants alone, but is rather a more intricate process. Specific genetic lineages of hospital-adapted strains have emerged, such as E. faecium clonal complex (CC) 17 and E. faecalis CC2, CC9, CC28 and CC40, which are high risk enterococcal clonal complexes. These are characterised by the presence of antibiotic resistance determinants and/or virulence factors, often located on pathogenicity islands or plasmids. Mobile genetic elements thus are considered to play a major role in the establishment of problematic lineages. Although enterococci occur in high numbers in certain types of fermented cheeses and sausages, they are not deliberately added as starter cultures. Some E. faecium and E. faecalis strains are used as probiotics and are ingested in high numbers, generally in the form of pharmaceutical preparations. Such probiotics are administered to treat diarrhoea, antibiotic-associated diarrhoea or irritable bowel syndrome, to lower cholesterol levels or to improve host immunity. In animals, enterococcal probiotics are mainly used to treat or prevent diarrhoea, for immune stimulation or to improve growth. From a food microbiological point of view, the safety of the bacteria used as probiotics must be assured, and data on the major strains in use so far indicate that they are safe. The advantage of use of probiotics in slaughter animals, from a food microbiological point of view, lies in the reduction of zoonotic pathogens in the gastrointestinal tract of animals which prevents the transmission of these pathogens via food. The use of enterococcal probiotics should, in view of the development of problematic lineages and the potential for gene transfer in the gastrointestinal tract of both humans and animals, be carefully monitored, and the advantages of using these and new strains should be considered in a well contemplated risk/benefit analysis.