Abstract: The stable and metastable states of different configurations of a mesoscopic loop in the form of an eight is studied in the presence of a magnetic field. We find that for certain configurations the current is equal to zero for any value of the magnetic field leading to a magnetic field independent superconducting state. The state with fixed phase circulation becomes unstable when the momentum of the superconducting electrons reaches a critical value. At this moment the kinetic energy of the superconducting condensate becomes of the same order as the potential energy of the Cooper pairs and it leads to an instability. Numerical analysis of the time-dependent Ginzburg-Landau equations shows that the absolute value of the order parameter changes gradually at the transition from a state with one phase circulation to another although the vorticity change occurs abruptly. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: Air particulate samples were collected at Chapiquiña near Arica (Chile) with a six-stage cascade impactor for about 17-day periods during a 31 month interval. Sixteen elements were determined by energy dispersive X-ray fluorescence analysis, and the elemental concentrations were subjected to principal factor analysis. The variability with time of the coarse particles was described by two factors both related to soil dispersion, whereas the fine particle variations could be explained by a third factor related to marine influence. Enrichment factors were compared with those obtained in other remote continental areas, in particular those of air particulate matter sampled at Chacaltaya, Bolivia. Results point to a negligible anthropogenic influence.

Abstract: The Maastricht limestone used for the construction of the 14th century O.L. Basilica in Tongeren, Belgium, is a light yellowish, porous, soft rock of the Late Cretaceous age. The limestone has a high carbonate content (> 95%); quartz and glauconite occur rarely. On the north side of the building, there is extensive growth of epilithic algae. On the south side, an assemblage of organisms was observed beneath the abiotic surface. This community, developed as a green layer 1 mm below the surface, is dominated by cyanobacteria. A moss was also present. The organisms were studied by transmitted light, phase contrast and scanning electron microscopy, and isolated in cultures. The cyanobacteria belong to the genera Synechococcus and Chroococcidiopsis, and the moss was identified as Tortula muralis Hedw. The organic matter present in the green layer was characterized in terms of molecular components using analytical pyrolysis. Pyrolysis products from polysaccharides and proteins, and evaporation/pyrolysis products from lipids, comprise the vast majority of identified compounds. The identification of specific biomarkers such as 7-methylheptadecane is further evidence of the presence of cyanobacteria. Phytenes and phytadienes are indicative of phototrophic organisms, as they are pyrolysis products from chlorophylls.

Abstract: The tetravalent and hexavalent selenium content of water samples can be determined by conventional energy-dispersive X-ray fluorescence after different preconcentration steps. Selenium values of nearly three-hundred different environmental and drinking water samples in Belgium are reported. The results are quite low, ranging from the detection limits up to 1 μg l−1. The concentration levels are compared to literature data and the speciation is discussed. The contribution of drinking water to the daily intake of selenium in Belgium ranges from less than 0.2 to 5%.

Abstract: Sensitive multi-element analysis techniques were applied to water samples collected in the vicinity of a small Zn-Pb-Cu sulfide mineralization in the region of Menez-Albot (Finistère, France). The variation of the trace-element content along a local stream shows the presence of the mineralization, mainly through a simultaneous positive anomaly in solution for a group of about 10 elements (e.g. Ni, Cu, Zn, As, Sb) which are connected with this type of mineralization. The anomaly decreases steeply due to the influx of swamp water rich in Fe, Mn and organic matter. The precipitation barrier is reflected in the stream sediment composition. Contamination from fertilizers was observed in some samples.

Abstract: Sixty-two samples of total sediments and the separated clay/silt size fractions were analysed by energy-dispersive X-ray fluorescence spectrometry to evaluate the pollution level and the trends in samples collected along the Belgian coast over a period of 6 yr and at four stations located in the Scheldt estuary where two of these were sampled periodically for 4 yr. Three correction methods for grain size effects were applied, either to the bulk sediment samples or to the clay/silt size fractions, and the results were compared. Local variations on the concentrations in some of the elements determined were used to establish whether they result from an anthropogenic or natural origin. The level of pollution was assessed as a function of the location, sampling date, and depth.

Abstract: Sensitive multi-element analysis techniques together with major-element and isotopic analyses were applied to spring, mine and surface waters in the vicinity of an important known zinclead deposit in a carbonate environment, in the Les Malines area (Gard, France). Both the dissolved and suspended phases were investigated, and concretions and sediments were also considered in some cases. This methodological test shows that the ore body leaves various clear fingerprints, such as the Zn, As, Sb, Pb and U levels in the dissolved phase, the sulfate increment and the δ 34S. Some of the elements in solution are controlled by slightly soluble compounds, e.g. Zn by smithsonite and hydrozincite, Ba by barite, and Pb by hydrocerussite. Mapping the saturation indices for these elements appears useful for displaying the hydrogeochemical anomaly.

Abstract: Between 15 January and 26 February 1987, 51 fine and coarse mode aerosol samples were collected at the Universidad de Santiago de Chile Planetarium using a dichotomous sampler. The samples were analyzed by X-ray fluorescence for up to 17 elements (Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br and Pb). Aerosol particles were individually studied by Electron Probe Microanalysis (EPMA) and Laser Microprobe Mass Analysis (LAMMA). The data set consisting of aerosol elemental concentrations and meteorological variables was subjected to Principal Factor Analysis (PFA), allowing the identification of six fine mode particle source classes (soil, industrial, sulfate particles, traffic, residual oil, wood-burnings), and five coarse mode particle source classes (soil, industrial, traffic, residual oil, sulfate particles). Both PFA solutions explained about 81 and 90% of the total variance in the data set, respectively. The regression of elemental mass concentrations on the Absolute Principal Factor Scores allowed the estimation of the contribution of the different source classes to the Santiago aerosol. Within the fine fraction, secondary SO42− particles were responsible for about 49% of the fine mode aerosol mass concentration, while 26, 13, 6.4 and 5.6% were attributed to wood-burning/car exhausts, residual oil combustion, soil dust/metallurgical, and soil dust/wood-burning releases, respectively. The coarse fraction source apportionment was mainly dominated by soil dust, accounting for 74% of the coarse mode aerosol mass concentration. A composite of soil dust and industrial release accounted for 13%; a composite of secondary sulfates contributed with 9%; a composite of soil dust and automotive emissions, and secondary sulfates were responsible for 4 and 0.03% of the coarse aerosol mass concentration, respectively. EPMA results are in satisfactory agreement with those from the bulk analysis and allowed the identification of eight particle types in both fine and coarse mode aerosols, pertaining to different source classes, namely soil, seaspray, secondary SO42−, metallurgical emissions and biomass burning release. EPMA also evidenced that one of the most abundant particle types corresponded to marine aerosol, having an average diameter of 0.7 μm for the fine mode and 2.2 μm for the coarse mode aerosol. LAMMA results indicate that, in fact, seaspray has been transported into the city of Santiago de Chile airshed, suffering several transformations and a sulfur enrichment. This analytical technique also provided evidence of the abundance of carbon-rich particles, which were not detected by either the bulk X-ray analysis or EPMA; they are probably due to fossil-fuel combustion releases.

Abstract: A remote site in the Namib Desert was selected for sampling background aerosols in southern Africa, as one of a wide network of stations spanning the Southern Hemisphere in a programme designed to measure the background concentrations of trace elements in the atmosphere. A series of samples was collected over a 6-month period using a single-orifice cascade impactor, which fractionated the particles into six size groups. Analysis was performed using particle-induced X-ray emission (PIXE), yielding results for S, Cl, K, Ca, Ti, Mn, Fe, Br and Sr, and occasionally also for V, Cr, Ni, Cu, Zn and Pb. No direct correlations with wind direction were observed excluding strong local or regional sources of particles. K, Ca, Ti, Mn and Fe can be identified with a dust dispersion source. Cl, large particle S and Br, and part of the K and Sr are derived from sea spray. Relative to the soil components small particle K is not enriched as it normally is in regions with less scarce vegetation. Cr, V, Ni, Cu, Zn and Pb concentrations and enrichments in the aerosol are lower than practically all values measured at any other location hitherto. The concentration of the small particle sulphur, 200 ng m−3, is believed to be related to anaerobic conditions and plankton blooms in the ocean upwelling zones off Namibia.

Abstract: Dry deposition velocities have been calculated using three different approaches. Turbulent wind profile theory has been used to predict the drag coefficient, wind speed and friction velocity at 10 m height when the wind speed is measured at a higher altitude. The resulting parameters were introduced in a two-layer deposition model. The second approach was the well-known model of Slinn and Slinn (1980, Atmospheric Environment 14, 1013-1016), whereas the third corresponded to the model published by Williams (1982, Atmospheric Environment 16, 1933 1938). Results point to clear differences. However, in a field experiment carried out at the Southern Bight of the North Sea, all three approaches show relatively comparable results. The role played by the size distribution of atmospheric particulate matter is essential. In our case any of the three models could have given satisfactory outcomes taking into account the wide spread of the experimental results cited in the literature for the same airshed.

Abstract: The optical behavior of a four-level system in a ring cavity driven by two coherent laser fields is studied. One laser field is treated as the incident field and the other the control field, respectively. It is found that there is optical transparency when the difference between the two frequency detunings of the incident and control fields from the corresponding atomic transition frequencies is zero. Optical bistability can be produced and controlled by increasing the magnitude of the frequency difference. The bistable hysteresis becomes larger when the frequency difference is increased. Further increase of the latter can lead to onset of multistability.