Abstract: In air particulate matter, sampled at a suburban site near the city of Antwerp, Belgium, more than 1500 individual Pb-containing aerosol particles with projected diameters between 0.2 and 15 μm were analyzed by automated electron probe X-ray micro analysis (EPXMA) for 26 elements and morphological features. Laser microprobe mass analysis (LAMMA) was used to detect elements with Z < 11, particularly ammonium compounds. The Pb-containing particles were classified into five main classes: Pb-sulfates, Pb-halides, soil related Pb, Pb associated with medium atomic number elements and Pb associated with high atomic number elements. Each class was divided into several distinct particle types, of which the abundance (in number and mass %), the mean projected particle diameter, and the chemical composition were determined. Auto exhaust products are responsible for Pb-sulfates and Pb-halides, making up respectively 66.7 and 27.8% by mass of the Pb-containing particles. Ammonium sulfate coatings were found to be present on nearly all Pb particles. The observations were correlated with daily concentrations of Pb and Br, obtained by particle induced X-ray emission analysis (PIXE).

Abstract: Data obtained by atomic absorption spectroscopy showed a selenium concentration of only 0.11 ppm as an average value for the most representative agricultural soils in Belgium. The selenium content in rye-grass grown on different soil types was between 0.05 and 0.11 ppm, and positively correlated with the soil selenium level. Addition of selenium in the form of selenite to the different soil types resulted in an increased selenium uptake by the plant. The ultimate concentration in the plant depended on the structural and chemical composition of the soil. Twelve other elements were determined in the soils by energy-dispersive X-ray fluorescence; none showed a strong correlation with the soil selenium content or with the selenium uptake by ryegrass.

Abstract: The sulphite and sulphate concentrations in weathering products of limestone and in wet and total deposition samples were measured by the modified West-Gaeke method and by ion chromatography. The sulphite content in the weathering crust and in the runoff rainwater of two historical buildings in Belgium, was always much lower than the sulphate content. The maximum sulphite to sulphate ratio was 2·5%. The sulphite concentration in wet and total deposition samples was in the low or sub ppm range except during two misty periods when the sulphite concentration was 6·8 and 21 mg litre−1. In those samples a high sulphate concentration was also found (nl. 57 and 137 mg litre−1, respectively).

Abstract: Few data are available on the inorganic atmospheric pollution in the rapidly expanding cities of South America, like Recife, on the Atlantic Coast of North-east Brazil. Therefore, the elemental composition of atmospheric aerosols was investigated for nine sites in the Recife conurbation and a fairly remote site in the area. Total aerosol samples were collected on cellulose filters for analysis by energy dispersive X-ray fluorescence and cascade impactors were used to collect the aerosols as a function of particle size for subsequent analysis by proton-induced X-ray emission. Local soil aliquots were also analysed. About eighteen elements were quantified in all cases. The average total atmospheric concentrations appeared to be well above natural levels but usually lower than, or comparable with, those of North American and European cities. Dispersal of sea spray and of local soil (often contaminated with, for example, Cu, Zn and Pb from industrial sources) contributes predominantly to the total atmospheric load in Recife. However, the particle size fraction results also indicated strong excesses in the small particle mode for S, K, V, Mn, Ni, Cu, Zn, Br and Pb, mainly in the downtown area. Again, the corresponding enrichment factors were only moderate in comparison with other published urban data.

Abstract: The structural phase transitions with electric-quadrupole long-range order in NpO2 (Fm (3) over barm-->Pn (3) over barm) and UO2 (Fm (3) over barm-->Pa (3) over bar) are analyzed from a group theoretical point of view. In both cases, the symmetry lowering involves three quadrupolar components belonging to the irreducible representation T-2g (Gamma(5)) of O-h and condensing in a triple-q structure at the X point of the Brillouin zone. The Pa (3) over bar structure is close to Pn (3) over barm, but allows for oxygen displacements. The Pa (3) over bar ordering leads to an effective electrostatic attraction between electronic quadrupoles while the Pn (3) over barm ordering results in a repulsion between them. It is concluded that the Pn (3) over barm structure can be stabilized only through some additional process such as strengthening of the chemical bonding between Np and O. We also derive the relevant structure-factor amplitudes for Pn (3) over barm and Pa (3) over bar, and the effect of domains on resonant x-ray scattering experiments.

Abstract: Recently discovered series of high Tc superconductors, characterized by the existence of two types of cations within the same layer, are presented. The first family concerns the mercury based cuprates, Hg(1-x)M(x)A(2)Ca(m-1)Cu(m)O(2m+2+delta), with A = Ba and/or Sr, which exhibit structures closely related to that of the thallium cuprates TlBa2Cam-1CumO2m+3. They differ from the thallium cuprates by a high oxygen deficiency at the level of the mercury layer. It is shown that cations such as M = Cu, Pb, Tl, Bi, Ce, Pr, Cr, V, Mo, W, Ti, Sr, Ca,... can partially substitute for mercury ions, stabilizing the structures. The cationic composition of the layer depends indeed on the nature of the M cation but also on that of the alkaline earth A. For given A and M cations, the a: value remains unchanged even when the number of copper layers varies. M and Hg cations are either statistically distributed over the same site or ordered. Different types of ordering have been detected. Another way of generating mixed layers is to shear periodically the structure, leading to the formation of the so called ''collapsed phase''. In the collapsed bismuth cuprates, bismuth and copper segments, a few octahedra long, alternate in strongly waving layers. In the collapsed oxycarbonates, carbonate groups and M cations are ordered within the intermediate layer so that they can be simply described from a partial and ordered substitution of carbon for Hg,TI, Bi and other M cations building the intermediate layer. The oxycarbonitrates (Y1-xCax)(n)Ba2nCu3n-1(C,N)O3O7n-3 can also be described as an ordered substitution of carbon for copper in the 123 matrix. The different families of superconducting materials which are generated by such mechanisms are described as well as the way the different species are distributed within the mixed layers. Their influence on the physical properties are discussed.

Abstract: The structural and melting properties of a quasi-one dimensional system of charged particles, interacting through a screened Coulomb potential are investigated. Depending on the density and the screening length, the system crystallizes in different lattice structures. The structural phase transitions between them are of first or second order. The melting of the system is studied through Monte Carlo simulations and reentrant behavior as a function of density is observed as well as evidence of anisotropic melting. (C) 2003 Published by Elsevier Ltd.

Abstract: In November 1984 in Makasar and the Flores Basin water samples were collected (T, S, dissolved O2, total CO2), bottom samples (sediment composition) and suspended matter (particle composition, particle size). A sediment trap was moored in the Flores Basin at 4600 m depth for nearly four months, covering the dry season. In the Flores Basin there are indications for bottom flow resuspending bottom material or preventing suspended material from settling; in Makasar Strait there is probably inflow of deep water both from the south and from the north, resulting in a very slow bottom water flor. Bottom deposits in Makasar Strait and the Flores Basin are predominantly terrigenous, with an admixture of organic carbonate and silica (mostly coccoliths). Volcanic material is primarily present near to the volcanoes in the south and reaches the deeper basins by slumping. In the suspended matter no volcanic particles and little planktonic material were found, although the latter form 10 to 15% of the top sediment and of the material deposited in the sediment trap. In suspension particles with a large concentration of tin (Sn) were found associated mainly with iron. They probably come from northern Kalimantan or northern Sulawesi. Suspended matter concentrations were mainly less than 0.5 mg·dm−3, only off the Mahakam river mouth were concentrations higher than 1 mg·dm−3. Particle size was erratic because of the variable composition of the coarser particles in suspension. Organic matter concentrations in suspension (in mg·dm−3) roughly follow the distribution of total suspended matter but organic content (in %) of the suspended matter does not show any trends. All organic matter in suspension is of marine origin except in the Mahakam river and estuary. Deposition rates, as estimated from the sediment trap results, are 150 mg·cm−2·a−1 for the total sediment, 26 mg·cm−2·a−1 for carbonate and 13 mg·cm−2·a−1 for organic matter. Flocs and fibres in suspension were only found in and below the Mahakam river plume that reaches ca 400 km from the river mouth to the southeast, and in surface waters associated with plankton (diatoms). The formation of these flocs (broken-up macroflocs or marine snow) is primarily related to particle concentration, turbulence, and the presence of organisms that produce sticky material or glue particles together.

Abstract: An investigation was made to determine the influence of the dumping of a 1000 ton day−1, on the average, of acid-iron waste from the titanium dioxide industry into the shallow but turbulent Southern Bight of the North Sea. This waste contains some 20% sulfuric acid and 2% iron. After the passage of the barge that discharges 10 ton of waste min−1 into its wake, the vertical and horizontal distributions of the pH, iron-concentration and turbidity were measured as a function of time. It appeared that a few seconds after the discharge and for a very brief period, the pH was down to approx. 4 and the Fe-concentration was 13 mg l−1. More than 1 min after the discharge a pH below 6 and an iron-level above 3 mg l−1 could not be detected anywhere. The measured factor for waste dilution by sea water, based on the observed acid and iron concentration in the waste and in the discharge track, were around 5000 after 5 min, 9000 after 10 min and 80,000 after 20 min. Before and long after the dumping, the total iron-concentration in this Southern Bight area was around 100 μg l−1, but this high level might be due to natural causes.