Volatiles from Thymbra and Thymus species of the western Mediterranean basin, Portugal and Macaronesia

Thyme is the common name of many taxa belonging to the Thymbra and Thymus genera. Given the economic importance of thyme oils, many thyme species have been studied and their essential oils and other volatile-containing extracts chemically characterized. Thymbra and Thymus species are frequent in the west Mediterranean region, considered to be the centre of origin of the genus Thymus, and extend further westwards in the Iberian Peninsula and northwest Africa, to the Macaronesian region in the Atlantic Ocean. The present work gives an overview of the chemical composition of the volatiles from the taxa of these two genera occurring in the above geographic area.     

Analysis of phenylpiperazine-like stimulants in human hair as trimethylsilyl derivatives by gas chromatography–mass spectrometry

A simple and sensitive procedure, using p-tolylpiperazine (pTP) as internal standard (IS), has been developed and validated for the qualitative and quantitative analysis of 1-(3-trifuoromethylphenyl)piperazine (TFMPP), 1-(3-chlorophenyl)piperazine (mCPP) and 1-(4-methoxyphenyl)piperazine (MeOPP) in hair. Drug extraction was performed by incubation with 1 M sodium hydroxide at 50 °C for 40 min, and the extracts were cleaned up using mixed-mode solid-phase extraction. The analytes were derivatized with N-methyl-N-(trimethylsilyl) trifluoroacetamide with 5% trimethylchlorosilane and analysed by gas chromatography–mass spectrometry in the selected ion monitoring mode. The method was linear from 0.05 (lower limit of quantitation) to 4 ng mg⁻¹, with correlation coefficients higher than 0.99 for all the compounds. Intra- and interday precision and accuracy were in conformity with the criteria normally accepted in bioanalytical method validation, and the sample cleanup step presented a mean efficiency higher than 90% for all the analytes. Due to its simplicity and speed, this method can be successfully applied in the screening and quantitation of these compounds in hair samples, and is suitable for application in forensic toxicology routine analysis.     

Concentration multi-échelles de courbure dans des fibres de Milnor

Résumé. Etant donné un germe de morphisme analytique complexe à fibre réduite, nous étudions la manière dont la courbure de Lipschitz-Killing de la fibre de Milnor pour la métrique induite par celle de se concentre asymptotiquement, lorsque , dans l'intersection de cette fibre avec des boules dont les centres peuvent être décrits mais surtout dont les rayons sont de la forme où les des nombres rationnels dont la collection ne dépend que de la topologie du plongement dans du germe de courbe plane réduite . Received: May 29, 1998.     

Ultrasound-assisted extraction and determination of tartaric and malic acids from grapes and winemaking by-products

The optimization of an ultrasound-assisted extraction (UAE) method for tartaric and malic acids from grape derived samples is shown. A fractional factorial experimental design allowed for the determination of the effects of seven extraction variables. Relationships between all the variables were examined. By applying graphical analysis, the best extractions conditions were obtained. The most important variables were the extracting liquid and the extraction temperature. Later, a central composite design was applied for optimizing the temperature and the composition of the extracting liquid. The optimized method was applied to grapes and to winemaking by-products. The repeatability of the method was studied and the recovery of tartaric and malic acids was established. Organic acids quantification was done by liquid chromatography (LC) using a post-column buffer and a conductivity detector.     

The preopt package for pre-optimization of gradient elutions in high-performance liquid chromatography

A theoretical model is described for quick pre-optimization of binary multistep gradient elutions in liquid chromatography. This model utilizes experimental retention-time data under isocratic elution conditions for different proportions of organic modifier in the mobile phase, and simulates the position of the peaks in the chromatogram by calculation of the average velocity of the peaks through the column. Optimization is done for multistep gradients by means of the simplex algorithm. The results must then be confirmed experimentally. Results are given demonstrating the power and validity of the model in the resolution of complex mixtures. The whole process done on a micro-computer with the PREOPT package usually takes about 30 min, without requiring user participation or chromatographic instrumentation.     

Market Power Issues in Bid-Based Hydrothermal Dispatch

The objective of this work is to investigate market power issues in bid-based hydrothermal scheduling. Initially, market power was simulated with a single stage Cournot–Nash equilibrium model. In this static model the equilibrium was calculated analytically. It was shown that the total production of N strategic agents is smaller than the least-cost solution by a factor of (N/(N+1)). Market power analysis for multiple stages was then carried through a stochastic dynamic programming scheme, where the decision in each stage and state is the Cournot–Nash equilibrium of a multi-agent game. Case studies with data taken from the Brazilian system are presented.     

“Green Electrodes” Modified with Au Nanoparticles Synthesized in Glycerol,as Electrochemical Nitrite Sensor

A new environmentally friendly Au nanoparticles (Au NPs) synthesis in glycerol by using ultraviolet irradiation and without extra‐added stabilizers is described. The synthesis proposed in this work may impact on the non‐polluting production of noble nanoparticles with simple chemicals normally found in standard laboratories. These Au NPs were used to modify a carbon paste electrode (CPE) without having to separate them from the reaction medium. This green electrode was used as an electrochemical sensor for the nitrite detection in water. At the optimum conditions the green sensor presented a linear response in the 2.0×10^?7–1.5×10^?5 M concentration range, a good detection sensitivity (0.268 A L mol^?1), and a low detection limit of 2.0×10^?7 M of nitrite. The proposed modified green CPE was used to determine nitrite in tap water samples.     

Modelling of nano-alloying and structural evolution of bimetallic core-shell nanoparticles obtained via the microemulsion route

A Monte Carlo model has been developed to describe the formation of bimetallic nanoparticles via the microemulsion route. The motivation stems from the need to understand the kinetics of nanoparticle formation in microemulsion droplets in order to determine the best experimental conditions to synthesize a nanoparticle with a given structure. We focus our study on the influence of the homogeneous and heterogeneous critical nucleus sizes of both metals on nanoparticle structure, as well as the role played by the surfactant film flexibility. The study reveals that the final structure is sensitive to changes in the critical nucleus numbers, because these parameters determine the rate of nucleation. An increase in the difference between nucleation rates of both metals gives rise to a better segregation of metals in the final nanoparticle. Likewise, as long as the formation of heterogeneous seeds is faster, the degree of alloying is greater. Finally, a fast material intermicellar exchange leads to a better mixture of metals, so the influence of the critical nucleus sizes on nanoparticle structure becomes less pronounced as the flexibility of surfactant film is increased.     

Operation of a 32 GHz gyrotron

The design and operation of a 32 GHz pulsed gyrotron are reported. The device is step-tuned between the TE_1,2 (24.16 GHz) and TE_0,2 (31.78 GHz) modes with cathode voltages ranging from 30 to 40kV and beam current up to 5.0A. Experimental frequencies are in close agreement with the self-consistent calculated values and in the TE_2,2 resonator mode an output peak power of 6kW corresponding to an 18% efficiency was measured by using a fast response calorimeter with a thermal sensitivity of 0.1°C/Wmin.     

Imposex and organotin body burden in the dog‐whelk (Nucella lapillus L.) along the Portuguese coast

Nucella lapillus imposex—superimposition of male characters onto prosobranch (a subclass of gastropod molluscs) females—and organotin female body burden were surveyed on the Portuguese coast, from Vila Praia de Âncora (northern limit) to Praia da Luz (southern limit), at 17 sampling stations, between May and August 2003. The vas deferens sequence index (VDSI), the relative penis size index (RPSI), the percentage of females affected with imposex (%I) and the percentage of sterile females (%S) were used to assess the level of imposex at each site. VDSI, RPSI and %I were 0.20–4.04, 0.0–42.2% and 16.7–100.0%, respectively. Sterile females were found at stations 2 (6.2%), 5 (4.0%) and 7 (5.0%). Tributyltin (TBT) and dibutyltin (DBT) female body burdens were 23–138 and <10–62 ng Sn/g dry weight, respectively. TBT female body burden was significantly correlated with RPSI and VDSI [Spearman rank order linear correlation: RPSI vs TBT body burden (b.b.) r = 0.71, p < 0.01; VDSI vs logTBT body burden r = 0.71, p < 0.01]. Imposex and TBT b.b. were highest at sites located in the proximity of harbours, where TBT leaching from antifouling paints is more intense owing to the high concentration of ships and dockyard activities. Copyright © 2005 John Wiley & Sons, Ltd.