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  • Author or Editor: A. León x
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Abstract  

Let {X t : 0 ≦ t ≦ 1} be a centered stationary Gaussian process, with correlation function satisfying the condition ρ(t) = 1 − t β L(t), 0 < β < 2, and let L be a slowly varying function at zero. Observing the process at points i/N, i = 0,1,..., N and considering ¦X i/NX (i-1)/N¦p with p > 0, we study the properties of the Donsker line associated with p-th order variations

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{bbm} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\sum\limits_{i = 1}^{[N{\text{ }}t]} {|X_{i/N} } - {\text{ }}X_{(i - 1)/N} |^p$$ \end{document}
. We also study the relationship between the number of crossings of a regularization of the initial process and the local time of the initial process. The results depend on the values of β.

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Abstract  

Fecal radiobioassay is a sensitive tool to estimate intake of radionuclides, especially for insoluble or poorly absorbed actinides. To increase efficiency and reduce turnaround time, improvements were introduced in the sample digestion step of a fecal bioassay method to rapidly detect Pu and Am. The acid- and microwave-digestion of the spiked fecal samples (5–10 g) were effectively completed in 1 h. The turnaround time for the sample analysis was minimized to 6 h. The average recoveries for Pu and Am were 35% and 60% for artificial fecal samples, respectively. Much better recoveries for Pu and Am were obtained for natural fecal samples. Observed relative biases for Pu and Am were marginally in the range of -0.25 to +0.50. The relative precision values for both radionuclides were, however, within the performance index of 0.4. This rapid fecal method is a potential candidate for an acceptable quantitative radiobioassay and screening method for the suspected Pu/Am exposures.

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Abstract  

U, Th and Ra isotopic activities have been measured in water and sediment samples collected over three years from the Guadalquivir river channel (South of Spain). The study of the radioactivity levels and activity ratios evolution in space and time has provided information on the behavior of the radionuclides mentioned above in the estuarine and non-estuarine zones of the river.

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Abstract  

All complexes of the series [MO2L2]+ (M=Tc, Re; L=ethylenediamine (en), 1,3-diaminopropane (1,3-dap)) have been synthesized and their chemical reactivities investigated. The following properties were studied: stability of the aqueous solutions at different pH values, substitution kinetics, lipophilicity and protein binding. The complexes show very similar reactivity in aqueous solution. From a radiopharmaceutical point of view, no significant difference in their in vivo behavior is expected.

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Abstract  

The occurrence of anomalous enhancements of U-isotope activities in the surrounding environment of a phosphate fertilizer factory complex at the southwest of Spain has been established. It seems that significant amounts of U, released by such industries, are being accumulated in the environment, which may substantially contribute to the collective radiation dose received by the local population.

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Abstract  

An extensive study on the distribution of natural radionuclides in an estuarine ecosystem located in Southwestern Spain is presented. This environment is highly affected by the wastes released by a phosphoric acid industry which uses phosphate rocks as raw material for fertilizer production. This rock has generally high concentrations of U and its daughters. The estuary is formed by two rivers, Odiel and Tinto, which have a common mouth into the Atlanic Ocean and a salt marsh (Odiel marsh) affected by the income of Odiel riverwaters. This river receives directly the liquid and part of the solid (gypsum) wastes released from the industries. Besides that, most of the phosphogypsum wastes are stored in uncovered piles at the right margin of the Tinto river. The study has concluded that the wastes from such industries are the cause of the enhanced concentrations found at the bed of both river channels as well as the enhancement found in surface soils in certain zones of the Odiel wet marshland. Indeed, the Northern marsh and the Mojarrera channel at the Odiel marsh seem to be the main sinks of the contaminant released by the phosphoric acid industry.

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Abstract  

In estuarine environments there are important spatial and temporal changes in both salt and suspended load concentrations. An experimental procedure have been developed to produce kinetic parameters being representative of the natural environment studied, and we have investigated the effect of salinity and suspended load concentration to the kinetics of the uptake. These results are encouraged by recent advances in environmental modelling concerning to radionuclide dispersion in aquatic natural systems and involving non-equilibrium processes. Experiments are carried out with unfiltered water samples from the Odiel estuary (Southwest of Spain), with133Ba tracer to illustrate experimental procedures.

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Abstract  

A series of Tc/V/ cationic complexes was synthesized by electrochemical reduction of TcO 4 . The electrolysis was performed in aqueous media containing amines as ligands: en, dien, trien and 1,3-dap*. The combination of different techniques allows to propose the general formula [TcO2/amine/2]+ for these compounds. Electrodeposition of TcO2 was a competitive reaction. The UV spectra were compared with those for other Tc/V/ amine complexes. The presence of two peaks, one in the range 303–312 nm and the other in 230–240 nm, could be verified. The latter was markedly sensitive to pH changes. Preliminary studies showed that kinetic stability decreases in the sequence en, 1,3-dap, trien, dien. The decomposition rate increased when the pH was lowered.

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Abstract  

Concentrations of U- and Ra-isotopes in rainwater samples taken in the South Spanish atmospheric environment during the years 1986, 1987 and 1988 are presented. Such data have been obtained by applying a simple method for the simultaneous determination of such radionuclides from the same rainwater sample. Ra is firstly coprecipitated as Ba–Ra sulfate. Then two alternatives can be used for U analysis: a coprecipitation of U with Fe, followed by a selective redissolution of the precipitate with ammonium carbonate, or a solvent extraction technique by using tributyl phosphate. Levels of 0.99 to 1.81 g/l, 3.4 to 17.9 mBq/l and 0.5 to 5.5 mBq/l, respectively for U,226Ra and224Ra are found during the studied time period. The dependence of such concentration variability on meteorological parameters is discussed.

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Abstract  

Electrolytic pertechnetate reduction at inert electrodes was studied as an alternative procedure for synthesizing Tc complexes. Pertechnetate reduction was carried out in aqueous media using different aminated ligands /en, dien, trien and 1,3-dap/ forming [TcO2/amine/2]+ type complexes. Simultaneously with synthesis of the desired Tc complex, TcO2 was electrodeposited onto the cathode. Conversion of TcO 4 to Tc complex and TcO2 was studied as a function of several variables /kind and concentration of supporting electrolyte, ligand concentration, pH, current and electrolysis time/.

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