Comparison of Methods to Estimate the Time‐to‐failure Distribution in Degradation Tests

Degradation tests are alternative approaches to lifetime tests and accelerated lifetime tests in reliability studies. Based on a degradation process of a product quality characteristic over time, degradation tests provide enough information to estimate the time‐to‐failure distribution. Some estimation methods, such as analytical, the numerical or the approximated, can be used to obtain the time‐to‐failure distribution. They are chosen according to the complexity of the degradation model used in the data analysis. An example of the application and analysis of degradation tests is presented in this paper to characterize the durability of a product and compare the various estimation methods of the time‐to‐failure distribution. The example refers to a degradation process related to an automobile's tyre, and was carried out to estimate its average distance covered and some percentiles of interest. Copyright © 2004 John Wiley & Sons, Ltd.     

Perceived bridging and bonding social capital on Twitter: Differentiating between followers and followees

The present study investigates the influence of Twitter use and the number of followers and followees on perceived bridging and bonding online social capital. Data from a convenience sample of Twitter users (N = 264) indicate that bonding social capital is associated with the number of followers whereas bridging social capital is influenced by the number of followees. Thus, the directed friendship model on Twitter affects different forms of social capital differently. In addition, the study found a negative curvilinear effect of the number of followees on bridging and the number of followers on bonding online social capital. This indicates that the number of followees/followers has positive effects on online bridging/bonding social capital, but only to a certain point. The paper concludes with a discussion of the results in light of theoretical considerations and of implications for future research on the effects of Twitter on social capital.     

Automatic threshold estimation for data matching applications

Several advanced data management applications, such as data integration, data deduplication, and similarity querying rely on the application of similarity functions. A similarity function requires the definition of a threshold value in order to decide whether two different data instances match, i.e., if they represent the same real world object. In this context, threshold definition is a central problem. This paper proposes a method for estimating the quality of a similarity function. Quality is measured in terms of recall and precision calculated at several different thresholds. Based on the results of the proposed estimation process and the requirements of a specific application, a user is able to choose a suitable threshold value. The estimation process is based on a clustering phase performed over a data collection (or a sample thereof) and requires no human intervention since the choice of similarity threshold is based on the silhouette coefficient, which is an internal quality measure for clusters. An extensive set of experiments on artificial and real datasets demonstrates the effectiveness of the proposed approach. The results of the experiments show that in most cases the estimation error was below 10% in terms of precision and recall.     

Conflict Detection among Multiple Norms in Multi-Agent Systems

In open multi-agent systems (MAS), norms are being used to regulate the behavior of the autonomous, heterogeneous and independently designed agents. One of the main challenges on developing normative systems is that norms may be in conflict with each other. Norms are in conflict when the fulfillment of one norm violates the other and vice-versa. In previous works, the conflict checkers consider that conflicts can be detected by simply analyzing pairs of norms. However, there may be conflicts that can only be detected when we analyze several norms together. This work presents a conflict checker capable to detect conflicts between two or more norms at the same time. A new, more expressive normative language, represented by a BNF grammar, was developed to define norms and Conflict Checker was implemented in tool format. Two validation principles were applied: software testing and formal verification. The strategy thus developed emerges as a new syntax for definition and verification of conflicts in MAS.     

Online reconfiguration of component-based applications in PacoSuite

In this paper, we present an original approach for enabling online reconfiguration of component-based applications. This research fits into our component composition methodology PacoSuite, that makes use of explicit connectors between components, called composition patterns. Both components and composition patterns are documented by making use of a special kind of MSC. We propose an algorithm to check whether a new component can fulfill the role of an old component in a given composition pattern, without the need to revalidate the entire composition all over again. To enable online reconfiguration, we extend the documentation of a component with a new primitive that specifies when a component reaches a safe state. This approach enables to swap a component at run-time, while maintaining a consistent application.     

Conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid

We developed a conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA). The curing behaviors of diglycidyl ether of bisphenol A with triethylenetetramine (TETA), PAni.DBSA, and both amine compounds at different concentrations were investigated by differential scanning calorimetry (DSC). Epoxy/TETA systems containing PAni.DBSA presented two distinct exothermic peaks at 90°C due to the cure by TETA as a hardener and at 236°C related to PAni.DBSA as the curing agent. The presence of PAni.DBSA in the systems constituted by epoxy/hardener in stoichiometric proportions resulted in a decrease in the glass‐transition temperature of the epoxy matrix, as indicated by DSC and dielectric analyses. Electrical conductivity was determined in the epoxy/amine networks, with the TETA concentration kept constant and also in stoichiometric proportions of mixed hardener (TETA + PAni.DBSA) to epoxy resin. The last condition resulted in a higher electrical conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4059–4065, 2006     

Foodborne outbreak caused by Staphylococcus aureus: phenotypic and genotypic characterization of strains of food and human sources

An outbreak of staphylococcal food poisoning involving approximately 180 people occurred in Brodowski, S?o Paulo State, Brazil, in April 1998. Strains of Staphylococcus aureus isolated from foods and food handlers, implicated as the etiologic agent, were characterized with phenotypic (phage typing, antibiotic susceptibility test, and enterotoxin production), and genotypic (random amplified polymorphic DNA) characterization. Strains isolated from vegetable salad with mayonnaise sauce, broiled chicken, pasta in tomato sauce, and from the oropharyngeal secretions of five food handlers--A, B, C, H, and I--showed the same phage profile and antibiotic resistance. Random amplified polymorphic DNA generated 17 combined profiles with primers OPE-20 and OPA-7. The similarity of strains was analyzed by generating a dendrogram that classified the 59 strains of S. aureus into four major clusters (I, II, III, and IV). Strains from four food handlers (A, B, H, and I) and from vegetable salad with mayonnaise, broiled chicken, and pasta in tomato sauce showing the same phage type profile and resistance to antibiotics belonged to the same cluster and produced staphylococcal enterotoxin A. Therefore, these foods and food handlers were incriminated in the outbreak.     

Resin-bound aminofluorescein for C-terminal labeling of peptides: high-affinity polarization probes binding to polyproline-specific GYF domains

A polymer support for the solid-phase synthesis of C-terminally labeled carboxylic acids has been developed. Fluorophore-labeled peptides were constructed directly on the amino group of resin-bound aminofluorescein. Fmoc-protected aminofluorescein was coupled onto tritylpolystyrene, and the free phenolic hydroxyl positions of the fluorescein were blocked with suitable protecting groups. The mode of attachment was analyzed and found to be selective for the phenoxy ether linkage. The conditions for peptide synthesis on the labeling resin were investigated, and a small library of C-terminally labeled peptides was prepared. The fluorescence quantum yields of C-terminally labeled peptides were determined and indicated the suitability of the compounds for imaging and binding experiments. The obtained peptides were therefore investigated as fluorescence polarization probes. Two different proline-rich binding domains of the GYF family-CD2BP2 and PERQ2-were targeted by peptides labeled either C- or N-terminally. Reversible binding constants were determined by fluorescence polarization measurements and were verified by competition experiments with the corresponding unlabeled peptide. As a second control, the binding constants were measured by NMR titration experiments, recording the HSQC NMR spectra of (15)N-labeled proteins in the presence of the peptide polarization probes. Ligands with higher affinities than all others known previously were identified for both GYF domains. The competition assay with the developed fluorescent probe has a high statistical reliability and can thus be used for screening of GYF domain inhibitors.     

Alternative Synthesis of a Dialkylimidazolium Tetrafluoroborate Ionic Liquid Mixture and its Use in Poly(acrylonitrile‐butadiene) Hydrogenation

An alternative synthesis of a dialkylimidazolium ionic liquid mixture is developed in order to produce inexpensive solvents for biphasic hydrogenation of poly(acrylonitrile‐butadiene) rubbers (NBR) catalyzed by RuHCl(CO)(PCy₃)₂.