Determination of platinum and rhodium in dust and plant samples using microwave-assisted sample digestion and ICP-MS

The platinum group elements (PGEs), particularly platinum, palladium and rhodium, are nowadays increasingly emitted into the environment from automotive catalytic converters. Thus, a method for the determination of PGEs (especially platinum and rhodium) in dust and plant samples was developed. The developed method was based on microwave-assisted sample digestion and inductively coupled plasma mass spectrometric (ICP-MS) determination. Spectral interferences in ICP-MS determination were corrected using mathematical correction equations based on signal ratio measurement. In addition, platinum and rhodium concentrations in the digested dust samples were also determined after Te coprecipitation without correction of the interferences. The results for platinum and rhodium in reference materials (NIST SRM 2557, recycled monolith autocatalyst and BCR-723, road dust) were in good agreement with the certified values. Preliminary results for the anthropogenic platinum and rhodium emissions in Oulu, northern Finland, based on dust and plant samples, indicated a common traffic-related source of these metals.     

Pointwise behaviour of semicontinuous supersolutions to a quasilinear parabolic equation

A kind of supersolutions of the so-called p-parabolic equation are studied. These p-superparabolic functions are defined as lower semicontinuous functions obeying the comparison principle. Incidentally, they are precisely the viscosity supersolutions. One of our results guarantees the existence of a spatial Sobolev gradient. For p = 2 we have the supercaloric functions and the ordinary heat equation. Mathematics Subject Classification (2000) 35K55     

Pointwise behaviour of <Emphasis Type="Italic">M</Emphasis><Superscript>1,1</Superscript> Sobolev functions

Our main objective is to study Haj?asz type Sobolev functions with the exponent one on metric measure spaces equipped with a doubling measure. We show that a discrete maximal function is bounded in the Haj?asz space with the exponent one. This implies that every such function has Lebesgue points outside a set of capacity zero. We also show that every Haj?asz function coincides with a Hölder continuous Haj?asz function outside a set of small Hausdorff content. Our proofs are based on Sobolev space estimates for maximal functions.     

Absorption and photoluminescence properties of 4-substituted Alq3 derivatives and tris-(4-hydroxypyridinoanthrene)aluminum

A series of 4-substituted Alq₃ derivatives have been synthesized. Photophysical properties of the complexes in solution have been studied in detail. The results show that Hammett σ_p constants of the substituents have a linear correlation with the emission maximum values of the aluminum complexes. Substitution at the 4-position improves the color purity of the emission and it has also a strong influence on the quantum yields. A new type of Alq₃ derivative, tris-(4-hydroxypyridinoanthrene)aluminum, has a good quantum yield and high emission color purity.     

Soft X-ray contact microscopy of nematode Caenorhabditis elegans

Soft X-ray Contact Microscopy (SXCM) of Caenorhabditis elegans nematodes with typical length m and diameter m has been performed using the PALS laser source of wavelength m and pulse duration ps. Pulsed soft X-rays were generated using molybdenum and gold targets with laser intensities W/cm². Images have been recorded on PMMA photo resists and analyzed using an atomic force microscope operating in contact mode. Cuticle features and several internal organs have been identified in the SXCM images including lateral field, cuticle annuli, pharynx, and hypodermal and neuronal cell nuclei.Received: 18 February 2004, Published online: 29 June 2004PACS: 42.62.Be Biological and medical applications - 07.85.Tt X-ray microscopes - 87.59.Bh X-ray radiographyA color version of the figures is available in electronic form at .     

Smooth quasiregular mappings with branching

We give an example of a -smooth quasiregular mapping in 3-space with nonempty branch set. Moreover, we show that the branch set of an arbitrary quasiregular mapping in n-space has Hausdorff dimension quantitatively bounded away from n. By using the second result, we establish a new, qualitatively sharp relation between smoothness and branching.     

Source localization in complex listening situations: selection of binaural cues based on interaural coherence

In everyday complex listening situations, sound emanating from several different sources arrives at the ears of a listener both directly from the sources and as reflections from arbitrary directions. For localization of the active sources, the auditory system needs to determine the direction of each source, while ignoring the reflections and superposition effects of concurrently arriving sound. A modeling mechanism with these desired properties is proposed. Interaural time difference (ITD) and interaural level difference (ILD) cues are only considered at time instants when only the direct sound of a single source has non-negligible energy in the critical band and, thus, when the evoked ITD and ILD represent the direction of that source. It is shown how to identify such time instants as a function of the interaural coherence (IC). The source directions suggested by the selected ITD and ILD cues are shown to imply the results of a number of published psychophysical studies related to source localization in the presence of distracters, as well as in precedence effect conditions.     

Low-acceleration instability of a Bose-Einstein condensate in an optical lattice

We study a Bose-Einstein condensate in a one-dimensional accelerated optical lattice using the mean-field version of the Bose-Hubbard model. Reminiscent of recent experiments [M. Cristiani et al., Opt. Express 12, 4 (2004)], we find a new type of an instability in this system that occurs in the limit when the acceleration is small.     

Particle number fractionalization of an atomic Fermi-Dirac gas in an optical lattice

We show that a dilute two-species gas of Fermi-Dirac alkali-metal atoms in a periodic optical lattice may exhibit fractionalization of the particle number when the two components are coupled via a coherent electromagnetic field with a topologically nontrivial phase profile. This results in fractional eigenvalues of the spin operator with vanishing fluctuations. The fractional part can be accurately controlled by modifying the effective detuning of the electromagnetic field.     

Adsorption Kinetics of Complexes Formed by Oppositely Charged Polyelectrolytes

The objective of this study is to gain an understanding of the kinetics of adsorption of complexes formed in aqueous solution by oppositely charged polyelectrolytes. The properties of the complexes were characterized by means of dynamic light scattering and electrophoretic mobility and the reaction stoichiometry was studied by titration. The stoichiometry in the complexes depends on the polymer weight ratio w(p). Their point of zero charge (pzc) is shifted toward lower w(p) when simple cations of higher valence are added to the solution. The adsorption kinetics of the complexes on silica was studied by stagnation point reflectometry. The sign of charge of the complexes as well as the valence and concentration of simple cations governs the occurrence of adsorption in the electrolytes studied. Five different types of adsorption kinetics were found. Copyright 2001 Academic Press.