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11.
Ricardo J. N. Bettencourt da Silva Maria Filomena G. F. C. Camões 《Accreditation and quality assurance》2010,15(12):691-704
The dispersion of results from proficiency tests for the analysis of pesticide residues in foodstuffs suggests that improvements
in the compatibility of measurement results are needed. Currently observed divergences can make the evaluation conclusion
on foodstuffs compliance with certain legislation dependent on the consulted laboratory. This work discusses the origin and
impact of this lack of compatibility, following the metrological concepts presented at the latest version of the “International
Vocabulary of Metrology” (VIM3), thus allowing for a clear diagnostic of the problem. The reporting of results from different
measurement methods uncorrected for the observed analyte recovery makes them traceable to different “operationally defined
measurement procedures” (VIM3) and, therefore, not comparable. When results from different measurement methods are reported
corrected for analyte recovery, R, and R is different for spiked and incurred residues, measurement results may be not compatible if this effect is not considered
on the uncertainty budget. This discussion is illustrated with metrological models for any possible combination of “measurement
performance” and “maximum residue level”. These models are complemented with experimental data of the analysis of pesticide
residues in a sample of ginseng powder from a proficiency test. The adopted experimental design allowed the identification
of additional threats to metrological compatibility in this field. Solutions to the faced problem are discussed for practicability
and impact on regulatory issues. The use of a universal “reference measurement procedure” proves to be the most feasible way
of ensuring comparability of measurements in this field. 相似文献
12.
Francesca Guerriero Giovanna Miglionico Filomena Olivito 《European Journal of Operational Research》2014
The paper addresses restaurant revenue management from both a strategic and an operational point of view. Strategic decisions in restaurants are mainly related to defining the most profitable combination of tables that will constitute the restaurant. We propose new formulations of the so-called “Tables Mix Problem” by taking into account several features of the real setting. We compare the proposed models in a computational study showing that restaurants, with the capacity of managing tables as renewable resources and of combining different-sized tables, can improve expected revenue performances. Operational decisions are mainly concerned with the more profitable assignment of tables to customers. Indeed, the “Parties Mix Problem” consists of deciding on accepting or denying a booking request from different groups of customers, with the aim of maximizing the total expected revenue. A dynamic formulation of the “Parties Mix Problem” is presented together with a linear programming approximation, whose solutions can be used to define capacity control policies based on booking limits and bid prices. Computational results compare the proposed policies and show that they lead to higher revenues than the traditional strategies used to support decision makers. 相似文献
13.
Tiago P. Filomena Miguel A. Lejeune 《Journal of Optimization Theory and Applications》2014,161(1):308-329
We consider a probabilistic portfolio optimization model including fixed and proportional transaction costs. We derive a deterministic equivalent of the probabilistic model for fat-tailed portfolio returns. We develop a method which finds provably near-optimal solutions in minimal amount of time for industry-sized (up to 2000 assets) problems. To solve the mixed-integer nonlinear programming (MINLP) deterministic formulation equivalent to the stochastic problem, we design a mathematical programming-based warm-start heuristic. The tests show the computational efficiency of the heuristic which is more than an order of magnitude faster than Cplex in finding high-quality solutions. 相似文献
14.
Ivana Defrenza Alessia Catalano Alessia Carocci Antonio Carrieri Marilena Muraglia Antonio Rosato Filomena Corbo Carlo Franchini 《Journal of heterocyclic chemistry》2015,52(6):1705-1712
Starting from 2‐amino‐1,3‐mercaptobenzothiazoles recently reported ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h ), a series of the corresponding 2‐mercapto‐1,3‐benzothiazole isosters ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ) were screened for their in vitro antibacterial and antifungal activities. Results underline that the presence of the mercapto moiety at the 2‐position of the heterocyclic nucleus is crucial for activity against bacteria. The biological screening against Candida spp. identified commercial 2f as the most promising compound as antifungal against Candida albicans and tropicalis. Molecular modeling studies supported these results. Then, to enlarge structure‐activity relationship (SAR) studies on series 1 , newly synthesized compounds ( 1k , 1l , 1m , 1n , 1o , 1p ) were reported. All the compounds belonging to this series and bearing a bulky substituent at the 6‐position of the aryl moiety showed high antifungal activity. 相似文献
15.
Donato P Cacciola F Cichello F Russo M Dugo P Mondello L 《Journal of chromatography. A》2011,1218(37):6476-6482
The combined use of the state-of-the-art hybrid mass spectrometers together with high efficient liquid chromatography could surely be a useful tool for such a challenging task, as phospholipids (PLs) analysis. In this research, we used hydrophilic interaction liquid chromatography (150 mm×2.1 mm I.D., 2.7 μm d.p. partially porous column) to achieve the separation of major PLs classes in cow's and donkey's milk samples. Solid-phase extraction (SPE) was performed in order to pre-concentrate minor PLs from non polar lipids (triacylglycerols) and the recovery for the extraction method was assayed on a milk sample, fortified with 5 μg/mL of SM pure standard, and analyzed in triplicate. A value of 89.99% was calculated, with a coefficient of variation (CV%) of 1.93. A 70-min long stepwise gradient of water/acetonitrile afforded baseline separation of PLs classes, at 50 μL/min flow rate. Accurate detection by an ion trap-time of flight (IT-TOF) mass spectrometer (in both positive and negative ionization mode) allowed to fully characterize the distinctive phospholipid profile and fatty acid composition of cow's and donkey's milk, the latter being analyzed for the first time. Evaporative light scattering detection was further employed to attain the quantitative evaluation of major PLs classes identified, by the external calibration method using reference material solutions in the 5-200 μg/mL concentration range. Major difference between the two analyzed samples consisted in the total PLs amount, which in cow's milk was determined as over 20-fold higher than the donkey's. 相似文献
16.
Assis AC Couto N Duarte MF Rodrigues P Barros MT Costa ML Cabral BJ Fernandez MT 《Journal of mass spectrometry : JMS》2011,46(7):696-704
The relevance of metal interactions with azides has led us to the study of the complexation of some transition metals, nickel and cobalt, by azidoacetone by means of electrospray ionization mass spectrometry (ESI-MS). Complexes were obtained from solutions of NiCl(2) and CoCl(2) , in methanol/water. Nickel was electrosprayed with other counter ion, bromide (Br), as well as other solvent (ethanol/water). For nickel and cobalt, the complexes detected were single positively charged, with various stoichiometries, some resulted from the fragmentation of the ligand, the loss of N(2) being quite common. The most abundant species were [Ni(II)Az(2)X](+) where X = Cl, Br and Az = azidoacetone. Some of the complexes showed solvation with the solvent components. Metal reduction was observed in complexes where a radical was lost, resulting from the homolytic cleavage of a metal coordination bond. Collision-induced dissociation (CID) experiments followed by tandem mass spectrometry (MS-MS) analysis were not absolutely conclusive about the coordination site. However, terminal ions of the fragmentation routes were explained by a gas-phase mechanism proposed where a C-C bond was activated and the metal inserted subsequently. Density functional theory calculations provided structures for some complexes. In [Ni(II)Az(2)X](+) species, one azidoacetone ligand is monodentate and the dominant binding location is the alkylated nitrogen and not the carbonyl group. The other azidoacetone ligand is bidentate showing coordination through alkylated nitrogen and the carbonyl group. These are also the preferential binding sites for the most stable isomer of [Ni(II)AzX](+) species. 相似文献
17.
Menichini F Tundis R Bonesi M de Cindio B Loizzo MR Conforti F Statti GA Menabeni R Bettini R Menichini F 《Natural product research》2011,25(8):789-799
The chemical composition of the essential oil of Citrus medica L. cv. Diamante peel obtained by hydrodistillation, cold-pressing and supercritical carbon dioxide extraction techniques was determined by GC/MS analysis. Forty-six components were fully characterised. Limonene and γ-terpinene were the major components of the oils obtained by hydrodistillation (HD) and cold-pressing (CP), while citropten was the major constituent in the oil obtained by supercritical carbon dioxide extraction (SFE). Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities were evaluated. The essential oil obtained by hydrodistillation exerted the highest inhibitory activity against BChE (IC?? value of 154.6 μg mL?1) and AChE (IC?? value of 171.3 μg mL?1. Interestingly, the oil obtained by cold-pressing exhibited a selective inhibitory activity against AChE. The essential oils have also been evaluated for the inhibition of NO production in LPS induced RAW 264.7 macrophages. The oil obtained by hydrodistillation exerted a significant inhibition of NO production with an IC?? value of 17 μg mL?1 (IC?? of positive control 53 μg mL?1). 相似文献
18.
Francesca Gladiali Massimo Grossi Filomena Pacella P. N. Srikanth 《Calculus of Variations and Partial Differential Equations》2011,40(3-4):295-317
In this paper we consider the problem $$\left\{ \begin{array}{ll} -\Delta u=u^p+\lambda u & \quad\hbox{ in }A,\\ u > 0&\quad \hbox{ in }A,\\ u=0 &\quad \hbox{ on }\partial A, \end{array}\right. $$ where A is an annulus of ${\mathbb{R}^N,N\ge2}$ and p?>?1. We prove bifurcation of nonradial solutions from the radial solution in correspondence of a sequence of exponents {p k } and for expanding annuli. 相似文献
19.
Ricardo J.N Bettencourt da Silva Helena Figueiredo M.Filomena G.F.C Camões 《Analytica chimica acta》2003,477(2):169-185
A methodology for the estimation of sample processing and sub-sampling performance based on the comparison of the global method experimental dispersion of results with the uncertainty estimated from developed models for the subsequent analytical steps is presented. This approach is a valuable alternative to the evaluation of adequate experimental information using a classical ANOVA, since the significance of the sample processing and sub-sampling is evaluated with a higher number of degrees of freedom for the same number of experimental assays, due to the high number of degrees of freedom associated with the uncertainty estimated for the subsequent analytical steps from the combination of the involved sources of uncertainty.Considering the construction of a model to describe the performance of the analytical steps following sample processing and sub-sampling over a broad concentration range, the experimental assays involved at the evaluation of the sample processing and sub-sampling can be performed at any concentration meeting the previously validated range and several months after the development of that model once its adequacy has been proven over time.This approach, which also allows the construction of a detailed performance model for the global analytical method over a broad concentration range, was applied to the determination of pesticide residues in apples by gas-chromatography with electron capture detector.Considering that no information was available regarding the samples heterogeneity, sub-sampling performance was evaluated considering a sample representing the worst expectable homogeneity. This was accomplished by spiking just one out of the 10 halves of apples processed in each sample.The developed model for the performance of the analytical method was successfully and easily applied to routine analysis through an automated link between the information generated by the chromatograph software with a file containing the model. 相似文献
20.
Giuseppina Castronuovo Vittorio Elia Filomena Velleca 《Journal of solution chemistry》1996,25(1):51-59
Enthalpies of dilution of binary and ternary aqueous solutions containing L-and D-proline, cis-L- and cis-D-4-hydroxy proline, trans-L-4-hydroxy proline, have been determined by flow calorimetry at 25°C. Pairwise self-and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. They are positive for solutions of unsubstituted prolines. On the contrary, upon the introduction of a hydroxy group, they become negative, reaching the largest value for the cis-L-lcis-D-4-hydroxy proline system. The results are interpreted in terms of preferential configurations, stabilized by interactions between the hydrophilic groups. 相似文献