Multiresidue determination of pesticides in drinking and related waters by gas chromatography/mass spectrometry after solid-phase extraction: interlaboratory study

As part of a project funded by the European Commission (EC) for the development and evaluation of multiresidue methods for analysis of drinking and related waters, 15 European laboratories evaluated a method using styrene-divinylbenzene co-polymer solid-phase extraction followed by gas chromatography/mass spectrometry. The main aim of the study was to evaluate whether the method meets the requirements of EC Directive 98/83 in terms of accuracy, precision, and detection limit for 22 pesticides according to the following requirements: limit of detection, < or = 0.025 microg/L; accuracy, expressed as recovery between 75 and 125%; and precision, expressed as repeatability relative standard deviation of the method of < 12.5% and as reproducibility relative standard deviation of the method of < 25%. Analyses for unknown concentrations were performed with fortified commercial bottled and tap waters. All laboratories were able to achieve detection limits of 0.01 microg/L for all pesticides except dimethoate and desisopropylatrazine (0.02 microg/L). The criteria for repeatability were met for all compounds except trifluralin, dimethoate, and lindane in bottled water and chlorpyrifos, dimethoate, and lindane in tap water. The criteria for reproducibility were met for all compounds except trifluralin, dimethoate, and lindane in bottled water and pendimethalin, chlorpyrifos, dimethoate, terbutryn, and lindane in tap water. In terms of accuracy, the method meets the requirements for all pesticides in both matrixes, except for lindane in bottled water and lindane and chlorpyrifos in tap water.     

Sharing risk through concession contracts

In this paper we model concession contracts between a public and a private party, under dynamic uncertainty arising both from the volatility of the cash flow generated by the project and by the strategic behaviour of the two parties. Under these conditions we derive three notions of equilibrium price and apply the model to a case study for one of the most important concession contracts in Italy.     

Log‐symmetric regression models: information criteria and application to movie business and industry data with economic implications

This work deals with log‐symmetric regression models, which are particularly useful when the response variable is continuous, strictly positive, and following an asymmetric distribution, with the possibility of modeling atypical observations by means of robust estimation. In these regression models, the distribution of the random errors is a member of the log‐symmetric family, which is composed by the log‐contaminated‐normal, log‐hyperbolic, log‐normal, log‐power‐exponential, log‐slash and log‐Student‐t distributions, among others. One way to select the best family member in log‐symmetric regression models is using information criteria. In this paper, we formulate log‐symmetric regression models and conduct a Monte Carlo simulation study to investigate the accuracy of popular information criteria, as Akaike, Bayesian, and Hannan‐Quinn, and their respective corrected versions to choose adequate log‐symmetric regressions models. As a business application, a movie data set assembled by authors is analyzed to compare and obtain the best possible log‐symmetric regression model for box offices. The results provide relevant information for model selection criteria in log‐symmetric regressions and for the movie industry. Economic implications of our study are discussed after the numerical illustrations.     

The Conjugacy Problem is Solvable in Free-By-Cyclic Groups

We show that the conjugacy problem is solvable in [finitelygenerated free]-by-cyclic groups, by using a result of O. Maslakovathat one can algorithmically find generating sets for the fixedsubgroups of free group automorphisms, and one of P. Brinkmannthat one can determine whether two cyclic words in a free groupare mapped to each other by some power of a given automorphism.We also solve the power conjugacy problem, and give an algorithmto recognize whether two given elements of a finitely generatedfree group are twisted conjugated to each other with respectto a given automorphism. 2000 Mathematics Subject Classification20F10, 20E05.     

Linking observables in perturbed topological field theories

The topological antisymmetric tensor field theory in n-dimensions is perturbed by the introduction of local metric dependent interaction terms in the curvatures. The correlator describing the linking number between two surfaces in n-dimensions is shown to be not affected by the quantum corrections.     

Use of ultrafast-laser-driven microexplosional for fabricating three-dimensional void-based diamond-lattice photonic crystals in a solid polymer material

Micro-sized void spheres are successfully generated in a solid polymer by use of a tightly focused femtosecond laser beam from a high-repetition-rate laser oscillator. Confocal reflection images show that the void spheres are longitudinal rotational symmetric ellipsoids with a ratio of long to short axes of approximately 1.5. Layers of void spheres are then stacked to create three-dimensional diamond-lattice photonic crystals. Three gaps are observed in the [100] direction with a suppression rate of the second gap of up to approximately 75% for a 32-layer structure. The observed first- and second-order gaps shift to longer and shorter wavelengths, respectively, as the angle of incidence increases.