Distribution and occurence of polycyclic aromatic hydrocarbons (PAHs) in sediments from the Mar Grande and Gulf of Taranto (Ionian Sea, southern Italy)

Marine sediments from the Mar Grande and Gulf of Taranto were analysed for 17 parent PAHs, with molecular weight from 128 to 278 Daltons. The analyses were performed by gas chromatography coupled to mass spectrometry (GC-MS). Total PAHs content in sediments ranged from 464 to 12522 microg kg(-1) dry wt for Mar Grande and from 593 to 72275 microg kg(-1) dry wt for Gulf of Taranto. The analytical results were compared with the published results for other coastal areas in the Mediterranean Sea. PAHs levels in the Gulf of Taranto sediments were the highest in the Mediterranean sea, while PAHs concentrations in Mar Grande were higher than the ones reported in the Adriatic and Cretan Sea and with the same order of magnitude of the ones known for coastal areas of the Western and the Eastern Mediterranean Sea. PAHs concentration ratios were consistent with the main source of these compounds, in most areas, being pyrolysis. Based on the comparison of both the individual and the total PAHs concentrations with proposed sediment quality guidelines, the acute biological effects on the marine organisms were probable, especially for the Gulf of Taranto, in which almost all PAHs concentrations in sediments were higher than the guidelines limit values. The statistical analysis effected by HCA and PCA methods was used in order to classify sediment samples and to identify accumulation areas.     

Estimates of majorizing sequences in the Newton-Kantorovich method: A further improvement

Let be an operator, with X and Y Banach spaces, and f^′ be Hölder continuous with exponent θ. The convergence of the sequence of Newton-Kantorovich approximations

     

Weak and strong convergence of the Ishikawa iterative process for a finite family of asymptotically nonexpansive mappings

In this paper, we introduce an Ishikawa implicit iterative process with errors for a finite family of N asymptotically nonexpansive mappings as follows:

     

Asymptotic Multivariate Dominance: A Financial Application

We propose a multivariate stochastic dominance relation aimed at ranking different financial markets/sectors from the point of view of a non-satiable risk averse investor. In particular, we assume that the vector of returns of a given market is in the domain of attraction of a symmetric stable Paretian law in order to take into account the asymptotic behaviour of the financial returns. We determine the stochastic dominance rule for stable symmetric distributions, where the stability parameter plays a crucial role. Consequently, the multivariate rule for ordering markets is based on a comparison between i) location parameters, ii) dispersion parameters, and iii) stability indices. Finally, we apply the method to the equity markets of the four countries with the highest gross domestic product in 2013, namely, the US, China, Japan and Germany. In this empirical comparison we examine the ex ante and ex post dominance between stock markets, either assuming that the returns are jointly (or conditionally, for a robust approach) Gaussian distributed, or in the domain of attraction of a stable sub-Gaussian law.     

Compatibility of activity coefficients estimated experimentally and by Pitzer equations for the assessment of seawater pH

Calibration of pH meters is usually performed with reference pH buffer solutions of low ionic strength, I ≤ 0.1 mol kg^?1. For seawater pH measurements (I ≈ 0.7 mol kg^?1), calibration buffers in high ionic strength matrix are required. The Harned cell, in association with the Nernst equation and a model for estimating the chloride ion activity coefficient, \(\gamma_{{{\text{Cl}}^{ - } }} ,\) is the basis of the primary method for pH assignment to reference pH buffers. The semi-empirical Pitzer model is, in principle, adequate to estimate \(\gamma_{{{\text{Cl}}^{ - } }}\) of complex solutions, namely seawater. Nevertheless, no assessment of the validity of the model for this matrix is known to the authors. This work aims at estimating the adequacy of the Pitzer model by assessing the metrological compatibility of mean activity coefficients, in this case \(\gamma_{ \pm } = \sqrt {\gamma_{{{\text{H}}^{ + } }} \gamma_{{{\text{Cl}}^{ - } }} }\) estimated experimentally with the Harned cell, \(\gamma_{ \pm }^{\text{Exp}} ,\) and using the Pitzer model, \(\gamma_{ \pm }^{\text{Ptz}}\). The measurement uncertainty considered in the compatibility test was estimated using the bottom-up approach, where components were combined by the numerical Kragten method after checking its adequacy. The compatibility of the estimated \(\gamma_{ \pm }\) was assessed for solutions with increasing complexity and an ionic strength of 0.67 mol kg^–1. \(\gamma_{ \pm }^{\text{Exp}}\) and \(\gamma_{ \pm }^{Ptz}\) are metrologically compatible for a confidence level of 95 % where the relative standard uncertainty of their difference ranged from 1.1 % to 3.1 % in all chloride solutions to approximately 6.3 % when sodium sulfate was also present. This led to assume the validity of the Pitzer model equations to estimate \(\gamma_{{{\text{Cl}}^{ - } }} ,\) required to define reference pH values of buffer solutions with high ionic strength.     

A model for the interactions involving hydrophilic structure maker solutes

Enthalpies of dilution of ternary aqueous solutions containing glucose and alkan-1-ols, alkan-1,2-diols and alkan-m,n-diols were determined at 298.15 K by flow microcalorimetry. The pair-wise cross interaction coefficients of the virial expansion of the excess enthalpies were evaluated: they are positive and depend in a complex manner on the length of the alkyl chain of the alkanols. The behaviour of these systems is interpreted in terms of preferential interactions between the hydrophilic groups of the alkanols and the destructured domain present on glucose.     

Chiral recognition in aqueous solutions: On the role of urea in hydrophilic and hydrophobic interactions of unsubstituted α-amino acids

Calorimetric and nuclear relaxation time measurements were carried out at 25°C on concentrated aqueous solutions of urea containing the L and D forms of the following -aminoacids: alanine, -aminobutyric acid, norvaline, and norleucine. Glycine was also studied under the same experimental conditions. The enthalpic interaction coefficients were rationalized according to the preferential configuration model. The trends of the homochiral coefficients at increasing concentration of urea underline an interaction mechanism not different from that occurring in water. Chiral recognition is the quantity more affected by the nature of the solvent. Among the amino acids studied, only norleucine presents this effect, which vanishes at the highest concentrations of urea because the attenuated electrostatic interactions cannot impose preferential configurations.     

Electrosynthesized, non-conducting films of poly(2-naphthol): electrochemical and XPS investigations

Advanced biosensors are frequently based on electrosynthesized polymeric films. In this context, the electrosynthesis mechanism underlying the electrochemical oxidation of 2-naphthol (2-NAP) in phosphate buffer at pH 7 on Pt electrodes has been investigated. The voltammetric behaviour suggested the formation of a non-conducting polymer (poly(2-NAP)) through an irreversible electrochemical process complicated by 2-NAP adsorption and fast electrode passivation. Repeat experiments showed the passive films to be strongly adherent to the Pt surface with thicknesses of approximately 10 nm, as estimated by in-situ electrochemical quartz crystal microbalance (EQCM) measurements and by X-ray photoelectron spectroscopy (XPS). The polymer structure was then investigated by XPS, which gave evidence of the presence of naphthalene rings bonded through poly(oxide) groups (C–O–C) and of quinonoid groups, probably present as the ends of polymeric chains. The polymer repeat unit and terminal groups derived by XPS analysis are in accordance with electrochemical results and with synthesis routes reported for phenol-derived compounds in aqueous solution. XPS also gave evidence of a large excess of oxygen, probably arising from water molecules entrapped by the polymeric chains, as suggested by angle-resolved XPS and thermal treatment of poly(2-NAP)/Pt film under ultra-high vacuum (UHV).