Vapor-particle partitioning of hydrocarbons in Western Mediterranean urban and marine atmospheres

An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon.     

Preisach modelling of nonlinear response in electrically biased lead zirconate titanate-based piezoceramics

The alteration of the high-field electrical permittivity (nonlinear response) of PZT-based ceramics when an electrical bias field is applied is reported in this work. Large differences are observed between soft and hard PZT behaviours. While in soft PZT a bias field does not modify the nonlinear behaviour, a notable dependence is verified in hard PZT. The Preisach model is satisfactorily used to describe experimental results. A distribution function containing the first terms of the Maclaurin development series of a function composed by two Gaussian-like functions of different amplitudes is proposed. The model gives a satisfactory explanation for the fact that the permittivity depends not only on the amplitude of the applied electric field, but also on the bias field, both for soft and hard ceramics and for poled or unpoled samples.     

The octet rule in chemical space: generating virtual molecules

We present a generator of virtual molecules that selects valid chemistry on the basis of the octet rule. Also, we introduce a mesomer group key that allows a fast detection of duplicates in the generated structures. Compared to existing approaches, our model is simpler and faster, generates new chemistry and avoids invalid chemistry. Its versatility is illustrated by the correct generation of molecules containing third-row elements and a surprisingly adept handling of complex boron chemistry. Without any empirical parameters, our model is designed to be valid also in unexplored regions of chemical space. One first unexpected finding is the high prevalence of dipolar structures among generated molecules.     

Weak forms of elimination of imaginaries

We study the degree of elimination of imaginaries needed for the three main applications: to have canonical bases for types over models, to define strong types as types over algebraically closed sets and to have a Galois correspondence between definably closed sets B such that A ? B ? acl(A) and closed subgroups of the Galois group Aut(acl(A)/A). We also characterize when the topology of the Galois group is the quotient topology. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Luminescence and compositional studies for the identification of “fire-setting” features at prehistoric mine La Turquesa (Catalonia,Spain)

Journal of Radioanalytical and Nuclear Chemistry - Modern mining activities often leads to destruction of archaeological records, making difficult to date the contexts and tools. In this work, a...     

An Effective Fluorescent Sensor for Choline-Containing Phospholipids

A set of weak CH⋅⋅⋅O interactions is responsible for the recognition of tetraalkylammonium ions (ball-and-stick structure) by the tripodal receptors depicted in the diagram, in which the binding pocket is lined with squaramide units. The association constants of the fluorescent receptors are remarkably high at about 10⁵ M ⁻¹ and can be used for signaling the presence of selected choline phospholipids. Z=RNH, where R=alkyl, arylamino; X⁻=BH₄⁻, Cl⁻, Br⁻, I⁻.     

A method for studying the diffusion of silver iodide particles in the atmosphere by means of I131

Zusammenfassung Es wird eine neue Methode entwickelt zur Erfassung der Diffusion des zur künstlichen Wetterbeeinflussung verwendeten AgI-Rauches in der freien Atmosphäre. Der durch Verwendung von I¹³¹ radioaktiv gemachte AgI-Rauch wird in speziellen Papierfiltern, die am Messflugzeug befestigt sind, aufgefangen; mittels eines chemischen Prozesses wird das AgI aus den Filtern gelöst und sodann auf eine Kernphotoplatte gebracht, wo die Zahl der -Spuren ein Mass für die Anzahl der in der Luft gefundenen AgI-Partikel darstellt.

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Paper presented at the 3rd International Symposium on Atmospheric Condensation Nuclei, Cambridge, England, July 16–18, 1958.     

Bifurcation of Limit Cycles from a Polynomial Non-global Center

Consider the planar ordinary differential equation , where the set consists of k non-zero points. In this paper we perturb this vector field with a general polynomial perturbation of degree n and study how many limit cycles bifurcate from the period annulus of the origin in terms of k and n. One of the key points of our approach is that the Abelian integral that controls the bifurcation can be explicitly obtained as an application of the integral representation formula of harmonic functions through the Poisson kernel. Dedicated to Professor Zhifen Zhang on the occasion of her 80th birthday