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W. E. Kuykendall Jr. L. E. Fite R. E. Wainerdi 《Journal of Radioanalytical and Nuclear Chemistry》1974,19(2):351-358
Résumé La mesure de traces d'éléments dans l'air ambiant a fait l'objet d'une attention accrue ces derniers mois, en raison d'un
intérêt grandissant pour les dangers en puissance pour la santé, qui résultent de l'exposition prolongée à certaines substances
toxiques. L'analyse par activation neutronique a été employée avec succès dans la recherche de traces d'éléments, et ce, pour
un grand nombre d'études de l'environnement; elle semble convenir de fa?on idéale pour la détermination non-destructive multi-élémentaire
de la composition de milieux de particules portées par l'air. Dans cet article, on rend compte des performances de l'analyse
instrumentale par activation neutronique comme on le montre dans le cas de 40 échantillons d'air filtrées provenant d'une
zone métropolitaine.
相似文献
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The use of column chromatography with Dowex AG50-X4 resin has allowed the quantitative separation of nicotinamide from its primary metabolite, N1-methylnicotinamide. Although the sensitivity is similar to earlier high-performance liquid chromatographic methods, this procedure allows multiple assays to be carried out simultaneously in a matter of minutes. This method should be useful to study nicotinamide methyltransferase activity in either whole cells or extracts, and is particularly well suited to screen column fractions for enzyme purification purposes. 相似文献
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Platonic gold nanocrystals 总被引:8,自引:0,他引:8
Kim F Connor S Song H Kuykendall T Yang P 《Angewandte Chemie (International ed. in English)》2004,43(28):3673-3677
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Law M Greene LE Radenovic A Kuykendall T Liphardt J Yang P 《The journal of physical chemistry. B》2006,110(45):22652-22663
We describe the construction and performance of dye-sensitized solar cells (DSCs) based on arrays of ZnO nanowires coated with thin shells of amorphous Al(2)O(3) or anatase TiO(2) by atomic layer deposition. We find that alumina shells of all thicknesses act as insulating barriers that improve cell open-circuit voltage (V(OC)) only at the expense of a larger decrease in short-circuit current density (J(SC)). However, titania shells 10-25 nm in thickness cause a dramatic increase in V(OC) and fill factor with little current falloff, resulting in a substantial improvement in overall conversion efficiency, up to 2.25% under 100 mW cm(-2) AM 1.5 simulated sunlight. The superior performance of the ZnO-TiO(2) core-shell nanowire cells is a result of a radial surface field within each nanowire that decreases the rate of recombination in these devices. In a related set of experiments, we have found that TiO(2) blocking layers deposited underneath the nanowire films yield cells with reduced efficiency, in contrast to the beneficial use of blocking layers in some TiO(2) nanoparticle cells. Raising the efficiency of our nanowire DSCs above 2.5% depends on achieving higher dye loadings through an increase in nanowire array surface area. 相似文献
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A simple method for the determination of volatile selenium compounds employing a gas chromatograph equipped with a photoionization detector is described. The method involves the direct injection of dimethylselenide (DMS) or dimethyldiselenide (DMDS) into the gas chromatograph; no derivatization of the sample was required. The photoionization detector was capable of detecting 60 pg (0.55 pmol) of DMS and 150pg (0.80pmol) DMDS. Sensitivity was 10-50 times greater with DMS and 4-20 times greater with DMDS when the photoionization detector was employed than when the flame ionization detector was employed. 相似文献
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Ji L Tan Z Kuykendall TR Aloni S Xun S Lin E Battaglia V Zhang Y 《Physical chemistry chemical physics : PCCP》2011,13(15):7170-7177
We synthesized Fe(3)O(4) nanoparticle/reduced graphene oxide (RGO-Fe(3)O(4)) nanocomposites and evaluated their performance as anodes in both half and full coin cells. The nanocomposites were synthesized through a chemical co-precipitation of Fe(2+) and Fe(3+) in the presence of graphene oxides within an alkaline solution and a subsequent high-temperature reduction reaction in argon (Ar) environment. The morphology and microstructures of the fabricated RGO-Fe(3)O(4) nanocomposites were characterized using various techniques. The results indicated that the Fe(3)O(4) nanoparticles had relatively homogeneous dispersions on the RGO sheet surfaces. These as-synthesized RGO-Fe(3)O(4) nanocomposites were used as anodes for both half and full lithium-ion cells. Electrochemical measurement results exhibit a high reversible capacity which is about two and a half times higher than that of graphite-based anodes at a 0.05C rate, and an enhanced reversible capacity of about 200 mAh g(-1) even at a high charge/discharge rate of 10C (9260 mA g(-1)) in half cells. Most important of all, these fabricated novel nanostructures also show exceptional capacity retention with the assembled RGO-Fe(3)O(4)/LiNi(1/3)Mn(1/3)Co(1/3)O(2) full cell at different C rates. This outstanding electrochemical behavior can be attributed to the unique microstructure, morphology, texture, surface properties of the nanocomposites, and combinative effects from the different chemical composition in the nanocomposites. 相似文献
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The microwave heating of two-dimensional slabs in a long rectangularwaveguide propagating the TE10 mode is examined. The temperaturedependency of the electrical conductivity and the thermal absorptivityis assumed to be governed by the Arrhenius law, while both theelectrical permittivity and the magnetic permeability are assumedconstant. The governing equations are the forced heat equationand the steady-state version of Maxwell's equation while theboundary conditions take into account both convective and radiativeheat loss. Approximate analytical solutions, valid for smallthermal absorptivity, are found for the temperature and theelectric-field amplitude using the Galerkin method. As the Arrheniuslaw is not amenable analytically, it is approximated by a rational-cubicfunction. At the steady state the temperature versus power relationshipis found to be multivalued; at the critical power level thermalrunaway occurs when the temperature jumps from the lower (cool)temperature branch to the upper (hot) temperature branch ofthe solution. In the steady-state limit the approximate analyticalsolutions are compared with the numerical solutions of the governingequations for various special cases. These are the limits ofsmall and large heat loss and an intermediate case involvingradiative heat loss. Results are also presented for a case wheredifferential cooling occurs on the different sides on the slab.An alternative heating scenario, where one end of the waveguideis blocked by a short, is also considered. The approximate solutionsare found for this geometry and compared in the small Biot-numberlimit to Kriegsmann (1997). Also, a control process is presented,which allows thermal runaway to be avoided and the desired finalsteady state to be reached. Various special cases of the feedbackparameters associated with the control process are examined. 相似文献
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Andreas?Lüthi Martin?A?Wikstr?m Mary?J?Palmer Paul?Matthews Tim?A?Benke John?TR?Isaac Graham?L?CollingridgeEmail author 《BMC neuroscience》2004,5(1):44