Förster energy transfer from poly(arylene–ethynylene)s to an erbium–porphyrin complex

We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φ_IR=4×10⁻⁴ is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er³⁺. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R₀, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials.     

New efficient catalysts for the aerobic oxidation of ethers

Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported.     

An optical bridge reflectometer for sensitive measurement of ion implantation dose

An instrument is described that can be used to monitor, with unprecedented sensitivity, changes in the optical reflectivity due to crystailine damage incurred during ion implantation. It is shown that at the shot-noise limit, changes in the optical reflectivity of silicon as small as 5·10^–7 can be measured in a 10 Hz bandwidth with a signal-to-noise ratio of 100, corresponding to an extrapolated uniform implantation dose of 5·10⁸ cm^–2 for ¹¹B⁺ at 50 keV in silicon.     

A Scanning Electron Microscopy study of water in soil

Cold stage Scanning Electron Microscopy (SEM) with a rapid cooling technique makes it possible to investigate the water phase within unsaturated porous media. It is thought that this technique preserves the main features of the micromorphology of the water menisci as it exists in the liquid phase in soils. Saddle-shaped elements, as well as pendular rings of water, were observed with concave and convex curvatures of the water-air interface. The hydraulic conductivity of an unsaturated soil may be inferred from SEM photographs. Observations of isolated water menisci indicate the existence of an immobile water domain. The surface geometry of the water menisci was analyzed quantitatively and surface tension and capillary pressure were determined.     

Improvement of the properties of polyarylate reinforced with liquid crystalline polymers

Blends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.     

Confinement of electrons and ions in a combined trap with the potential for antihydrogen production

Experiments with electrons and ions in a combined trap are reported. The unique capability to confine particles with opposite charge and very different mass simultaneously in the same spatial region makes the combined trap a promising device for future synthesis of antihydrogen.     

Time-scale and excitation energy partition in sequential binary decays induced by heavy-ion collisions at ≃6 MeV·A

We studied the sequential binary decay of the systems ³²S+⁴⁵Sc, ⁷⁶Ge, ⁸⁹Y, ⁵⁹Co, ⁶³Cu and ¹⁹F+⁶³Cu induced by collisions at ≃6 MeV·A. The two stages of the process have reaction-times compatible with the dynamics of different mechanisms. The study of the excitation energy partition shows that the reaction mechanism of the first step has influence on the de-excitation of the primary fragments producing two decay components which have different time scale. Received: 25 March 1997 / Revised version: 2 December 1997     

Antioxidant flavonol glycosides from Dorycnium hirsutum

Seven flavonol glycosides were isolated and identified from the aerial parts of Dorycnium hirsutum, together with catechin, D-pinitol, β-sitosterol, and stearic acid. The extracts and the isolated flavonol glycosides were evaluated for their antioxidant activity, using the DPPH test (radical scavenging) and the lipoxygenase assay (lipid peroxidation). Dedicated to the memory of Prof. I. Morelli. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 233–235, May–June, 2006.     

Accreditation of reference material producers: the example of IRMM's Reference Materials Unit

The potential approaches for third-party assessment of reference material producers are revisited and the activities of the Reference Materials (RM) Unit of the Institute for Reference Materials and Measurements (IRMM) to obtain accreditation to ISO Guide 34 and ISO 17025 are described. Accreditation was related to the Unit as all matrix RM activities of the institute are concentrated there. A management system was established that allows sufficient flexibility to be applicable to a wide range of RMs while being precise enough to ensure compliance with ISO Guides 30, 31 and especially 34 and 35. Accreditation was achieved in 2004 with independent scopes for testing and RM production and was confirmed and extended in 2005. The key aspects of the RM Unit's management system for RM production are presented. Presented at BERM-10, April 2006, Charleston, SC, USA