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901.
Gabriel Navarro Wolfgang Willems 《Proceedings of the American Mathematical Society》1997,125(6):1589-1591
Let and be distinct prime numbers and let be a finite group. If is a -block of and is a -block, we study when the set of ordinary irreducible characters in the blocks and coincide.
902.
The electrochemical response of carbon paste electrode was investigated containing an inorganic and a non-electroactive compound on which an electro- active organic molecule was adsorbed. Alizarin S was chosen as the test molecule adsorbed on 150 m2/g of alumina, because this molecule is either easily reduced or oxidized on carbon. The electrode response was found to be linear for low amounts of alumina containing a known amount of Alizarin S. The electrical yield was never higher than 50%, but was reproducible. An increasing alumina amount in the paste increased the response, but lowered the electrical yield. 相似文献
903.
Enachescu C Linares J Varret F Boukheddaden K Codjovi E Salunke SG Mukherjee R 《Inorganic chemistry》2004,43(16):4880-4888
The relaxation of the metastable state of the spin-crossover compound [Fe(L)(2)](ClO(4))(2).H(2)O, with L = 2,6-bis(pyrazol-1-ylmethyl)pyridine, populated by the LIESST (light induced excited spin state trapping) effect, has been investigated by magnetic measurements. The time dependence of the relaxation curve at several temperatures, starting from different initial states, is in the shape of stretched exponentials, and the thermal variation of the photostationary state under constant photoexcitation is progressive and reversible. These features are satisfactorily modeled by considering noninteracting two-level systems with a distribution of activation energies. A suggested origin for the distribution is the conformational flexibility of the nonplanar heterocyclic ligands. The effect of the intensity distribution during the LIESST process is also accounted for in a simple way. 相似文献
904.
Herrero M Navarro R García N Mijangos C Reinecke H 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4425-4430
Wet chemical modification reactions of PVC films in solvent/nonsolvent mixtures were performed. Three thiol compounds of different size and reactivity were used varying the solvent quality, temperature, and reaction times. The evolution of the concentration gradients within the films was studied using confocal Raman spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy. Surface selectivities were calculated and discussed in terms of the different relative reaction rate constants. 相似文献
905.
A time-based flow injection (FI) separation pre-concentration system coupled to an electrothermal atomic absorption spectrometer (graphite furnace) has been developed for the direct ultra-trace determination of selenite and selenate in drinking water. The pre-concentration of both forms of selenium is carried out onto a micro-column packed with an anionic resin (Dowex 1X8) that is placed in the robotic arm of the autosampling device. Selenite and selenate are sequentially eluted with HCl 0.1 M and HCl 4 M, respectively. The interference of large quantities of chloride during selenium atomisation is prevented by using iridium as a “permanent” chemical modifier. The features of the pre-concentration separation system for both species are: 53% efficiency of retention and an enhancement factor of 82 for a pre-concentration time of 180 s (sample flow rate=3 ml min−1) with HCl elution volumes of 100 μl. The detection limit (3 s) is 10 ng l−1 for the two species and the relative standard deviation (n=10) at the 200 ng l−1 level is 3.5% for selenite and 5.6% for selenate. The addition of selenite and selenate stock standard solutions to tap water samples yields a 97-103% recovery of both species. 相似文献
906.
907.
Cadmium (II) ion-catalyzed degradation of ampicillin in methanol at 20 degrees C has been studied. It has been observed that the rate values tend to saturate when the concentration of ampicillin or the metal ion is increased. The results obtained in the present study suggest that ampicillin degradation occurs through the formation of a 1:1 (SM) and 2:1 (S(2)M) ampicillin-metal complexes. These complexes decompose giving a single product (absorption maximum at 285 nm; ((p)=1.82x10(4) l mol(-1) cm(-1)) that has been isolated and identified (Cd(II) (L(2-))(2) (H(2)O)(4) Na(2)). The appearance of this product reflects a first order reaction with respect to the 1:1 complex, with a rate constant of 3.87x10(-2) min(-1) and the existence of an equilibrium between the 1:1 and 2:1 initial complexes. The equilibrium constant value, calculated from kinetic data, is 1.7x10(3) l mol(-1). 相似文献
908.
Fernández-Sánchez JF Segura Carretero A Cruces-Blanco C Fernández-Gutiérrez A 《Talanta》2003,60(2-3):287-293
This paper presents the characterization of polycyclic aromatic hydrocarbons (PAHs) in solid-surface fluorescence as the first step for obtaining new optical sensors for PAHs screening. The fluorescence properties of the EPA-PAHs (naphthalene, acenaphthene, acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo[a]anthracene, benzo[k]fluoranthene, benzo[b]fluoranthene, benzo[a]pyrene, indeno [1,2,3-cd]pyrene, benzo[g,h,i]perylene and dibenzo[a,h]anthracene) on five types of solid-surfaces were evaluated. The experimental variables (pH and percentage of organic solvent in samples) were studied, obtaining different possibilities for making individual sensors for some of these PAHs and the best conditions for developing sensors for PAH screening were also studied. 相似文献
909.
Julia Torres Carlos Kremer Helena Pardo Leopoldo Suescun Alvaro Mombrú Jorge Castiglioni Sixto Domínguez Alfredo Mederos Eduardo Kremer 《Journal of Molecular Structure》2003,660(1-3):99-106
Samarium complexes with glutamic acid containing cationic [Sm2(Glu)2(H2O)8]4+ units have been prepared and characterized by using elemental analysis, infrared absorption spectra and thermal analysis. In addition, the crystal and molecular structure of [Sm2(Glu)2(H2O)8](ClO4)4·3H2O was determined by X-ray diffraction. The presence of glutamic acid in the Sm coordination sphere allows the formation of a singular extended 2D arrangement. Sm atoms are nine coordinated, in a monocapped square antiprism geometry. They are connected by means of different μ-COO− bridges, involving - and γ-carboxylate groups of the amino acid. 相似文献
910.
The laser flash photolysis in a very low-pressure flow system with mass spectrometry detection technique was developed for the study of oxidation reactions of chlorofluorocarbons. In this work, we have studied the UV photolysis of O3 in the presence of Cl2 at room temperature, which presents two catalytic cycles of O3 depletion with efficiencies dependent on the partial pressures in the photoreactor. The ozone dissociation was initiated with fourth harmonic pulses of a Nd:YAG laser. The detection of the reactants and the final and intermediate reaction products was performed with real-time mass spectrometry. The variations of the O3, Cl2 and ClO concentration were measured. The equations system associated to a proposed kinetic scheme was solved numerically and excellent agreement with the experimental results was obtained. The results from this work allowed the determination of the wall loss rates of the O(1D), Cl and ClO radicals. 相似文献