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71.
Eduardo Ordó?ez-Regil Genoveva García-Rosales Omar Eduardo Gutiérrez-Mu?iz 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(1):197-201
Seawater contains trace elements in solution, such as lanthanides and uranium, which can act as natural tracers when they
flocculate to form the sediments of the seabed. Uranium is a special case because it is a radioactive element with isotopic
ratio close to 1.14 (234U/238U) in sea water. Uranium is also present in all fractions of sediments, although the isotopic ratio in each fraction takes
a specific value depending on its origin and surrounding environment. This work has been conducted in order to analyze lanthanides
and uranium in a core of sea sediments. It is focused on separating the fractions forming the layers along the depth profile
of the core sample so as to determine the 234U/238U activity ratios in fractions of organic matter, aquatic life skeletons and dissolved minerals. The Neutron Activation Analysis
showed the presence of U, Lu, Hf, Eu, Ce and Yb ranging up to 50 ppm while alpha spectrometry gave a series of 234U/238U activity ratios which are discussed on the basis of statistical analysis. 相似文献
72.
A selective novel reverse flow injection system with chemiluminescence detection (rFI-CL) for the determination of Cr(VI) in presence of Cr(III) with Dichlorotris (1,10-phenanthroline)ruthenium(II), (Ru(phen)3Cl2), is described in this work. This new method is based on the oxidation capacity of Cr(VI) in H2SO4 media. First, the Ruthenium(II) complex is oxidized to Ruthenium(III) complex by Cr(VI) and afterwards it is reduced to the excited state of the Ruthenium(II) complex by a sodium oxalate solution, emitting light inside the detector. The intensity of chemiluminescence (CL) is proportional to the concentration of Cr(VI) and, under optimum conditions, it can be determined over the range of 3-300 μg L−1 with a detection limit of 0.9 μg L−1. The RSD was 8.4% and 1.5% at 5 and 50 μg L−1, respectively. For the rFI-CL method various analytical parameters were optimized: flow rate (1 mL min−1), H2SO4 carrier concentration (20% w/V), Ru(phen)3Cl2 concentration (5 mM) and sodium oxalate concentration (0.1 M). The effect of Cr(III), Fe(III), Al(III), Cd(II), Zn(II), Hg(II), Pb(II), Ca(II) and Mg(II), was studied. The method is highly sensitive and selective, allowing a fast, on-line determination of Cr(VI) in the presence of Cr(III). Finally, the method was tested in four different water samples (tap, reservoir, well and mineral), with good recovery percentage. 相似文献
73.
Maria?Jo?o?Ferreira Javier?Gutiérrez García Jorge?PicadoEmail author 《Applied Categorical Structures》2011,19(2):469-487
We characterize normal and extremally disconnected biframes in terms of the insertion of a continuous real function in between
given lower and upper semicontinuous real functions and show this to be the common root of several classical and new insertion
results concerning topological spaces, bitopological spaces, ordered topological spaces and locales. 相似文献
74.
Mascaros PA Bazzicalupi C Bianchi A Giorgi C Valero MD Garzón RL Salido ML Valtancoli B 《Chemical communications (Cambridge, England)》2011,47(10):2814-2816
The synergistic action of the different binding groups of the polyfunctional HL receptor leads to the recognition of ADP over ATP in water, with a selectivity coefficient of up to 116, a phenomenon which is unprecedented in the context of synthetic receptors in water. The recognition is mostly due to the good matching between H(3)L(2+) and the protonated forms of ADP. 相似文献
75.
A. Baïri E. Zarco-Pernia J.-M. García de María J.-G. Bauzin N. Alilat N. Laraqi F. Gutiérrez 《Heat and Mass Transfer》2011,47(5):589-595
In the present study Nu-Ra-α correlations are proposed to calculate the steady-state natural convection heat transfer taking place in 2D air-filled cavities
of parallelogrammic section. The thermal conditions and the dimensions of the enclosures permit to cover a large range of
Rayleigh numbers, 1.7 × 103 ≤ Ra ≤ 3.0 × 109, suitable for diverse engineering applications. The two active walls of the cavities are kept vertical and isothermal at
hot and cold temperatures T
h
and T
c
respectively. Separated by a horizontal distance H, they have the same height H and are connected by a closed adiabatic channel whose upper and lower walls can be inclined at an angle α with respect to the horizontal, varying between −60° to +60°. That gives rise to a conducting or insulating cavity, in the
convective sense of the term (diode cavity). A computational model based on the finite volume method is used to solve the
governing equations. The large number of treated configurations led to propose Nu-Ra-α correlations for large ranges of Ra and α which can be applied to many engineering areas. The results of this numerical study have been successfully compared with
calculated and measured available data. 相似文献
76.
Iulian Preda Leonardo Soriano Daniel Díaz‐Fernández Guillermo Domínguez‐Cañizares Alejandro Gutiérrez Germán R. Castro Jesús Chaboy 《Journal of synchrotron radiation》2013,20(4):635-640
This work reports an X‐ray absorption near‐edge structure (XANES) spectroscopy study at the Ni K‐edge in the early stages of growth of NiO on non‐ordered SiO2, Al2O3 and MgO thin films substrates. Two different coverages of NiO on the substrates have been studied. The analysis of the XANES region shows that for high coverages (80 Eq‐ML) the spectra are similar to that of bulk NiO, being identical for all substrates. In contrast, for low coverages (1 Eq‐ML) the spectra differ from that of large coverages indicating that the local order around Ni is limited to the first two coordination shells. In addition, the results also suggest the formation of cross‐linking bonds Ni—O—M (M = Si, Al, Mg) at the interface. 相似文献
77.
Manuel Caetano Leonardo Padrino T Hector Gutiérrez Alberto J. Fernández Jimmy Castillo 《Mikrochimica acta》1998,128(3-4):169-175
Trace level vanadium determination is reported using a dual beam thermal lens spectrometer. The thermal lens was generated using an argon ion beam laser (pump beam) which was focused into a sample cuvette. The thermal lens signal (TLs) was monitored with a He-Ne laser beam and a photodiode detector. Multichannel averager software was developed for processing the transient TLs. The optimal set up, ensuring maximum sensitivity and linear calibration graphs was obtained using experimental design techniques. Under optimized conditions, the detection limits for aqueous and ethanol-water (2+3 v/v) and (4+1 v/v) vanadium complex solutions were, respectively, 0.0071 mg/l, 0.0065 and 0.0039 mg/l. 相似文献
78.
79.
Pérez-Cadenas Agustín López-Garzón Rafael Godino-Salido Luz Arranz-Mascarós Paloma Gutiérrez-Valero Dolores Carillo-Márquez Tomás 《Transition Metal Chemistry》2002,27(2):184-190
Reactions of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine with AgI and ZnII ions in 1/1 and 4/1 ligand-to-metal molar ratios, in aqueous media at 25 °C and 0.1 M KNO3 and KCl ionic strength, respectively, were followed by potentiometric techniques in order to determine formation equilibria for the complex species. The spectral curves, as a function of ligand-to-metal molar ratio at established pH values, were studied and four solid phases of stoichiometry: AgL·4H2O, Ag(HL)NO3·1.5H2O, AgL(OH)2K2·H2O and Zn(HL)2Cl2·7H2O were isolated and characterised by analytical, spectroscopic and thermal measurements. 相似文献
80.
Adolfo R. Gutiérrez 《Chemical physics letters》1980,74(2):293-297
A doubling of the origin is observed in the low-temperature electronic absorption spectrum of the complex carbonyl(pyridine)-phthalocyaninatoruthenium(II) in glassy matrices. The effect is studied by optical hole burning and results suggest a non-degenerate singlet ground state of near C2v symmetry to be invoked. 相似文献