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71.
A membrane filtration procedure for the preconcentration and atomic absorption spectrometric determination of Pb(II), Co(II) and Fe(III) ions in natural water samples has been established. Cellulose nitrate membrane filters (0.45 μm and 47 mm diameter) were used in all experiments. The procedure is based on chelate formation of the analyte metals with 1‐(2‐pyridylazo) 2‐naphtol (PAN) and on retention of the chelates on cellulose nitrate membrane filter. The cellulose nitrate membrane and analyte ions were completely dissolved by 500 μL of nitric acid at 85 °C on a hood and then metal determinations were performed by flame atomic absorption spectrometry. The method was applied to natural water samples for the determination of analyte ions with satisfactory results, e.g., recoveries > 95%, RSD's < 10%. 相似文献
72.
Gwinner G Hoffknecht A Bartsch T Beutelspacher M Eklow N Glans P Grieser M Krohn S Lindroth E Muller A Saghiri AA Schippers S Schramm U Schwalm D Tokman M Wissler G Wolf A 《Physical review letters》2000,84(21):4822-4825
Radiative recombination (inverse photoionization) is believed to be well understood since the beginning of quantum mechanics. Still, modern experiments consistently reveal excess recombination rates at very low electron-ion center-of-mass energies. In a detailed study on recombination of F6+ and C6+ ions with magnetically guided electrons we explored the yet unexplained rate enhancement, its dependence on the magnetic field B, the electron density n(e), and the beam temperatures T( perpendicular) and T( ||). The excess scales as T(-1/2)( perpendicular) and, surprisingly, as T(-1/2)( ||), increases strongly with B, and is insensitive to n(e). This puts strong constraints on explanations of the enhancement. 相似文献
73.
This paper investigates the behaviour of interest rates in Turkey using a two-regime TAR model with an autoregressive unit root. This method recently developed by Caner and Hansen [Threshold autoregression with a unit roots, Econometrica 69 (6) (2001) 1555–1596] allows to simultaneously consider non-stationarity and non-linearity. Our finding indicates that the interest rate is a non-linear series and is characterized by a unit root process over the period 1990:1–2006:5. 相似文献
74.
M. Tokman 《Journal of computational physics》2011,230(24):8762-8778
We propose a new class of the exponential propagation iterative methods of Runge–Kutta-type (EPIRK). The EPIRK schemes are exponential integrators that can be competitive with explicit and implicit methods for integration of large stiff systems of ODEs. Introducing the new, more general than previously proposed, ansatz for EPIRK schemes allows for more flexibility in deriving computationally efficient high-order integrators. Recent extension of the theory of B-series to exponential integrators [1] is used to derive classical order conditions for schemes up to order five. An algorithm to systematically solve these conditions is presented and several new fifth order schemes are constructed. Several numerical examples are used to verify the order of the methods and to illustrate the performance of the new schemes. 相似文献
75.
Esra Öztürk Nilgun Kalaycioglu Ozpozan Serkan Dayan 《Journal of Thermal Analysis and Calorimetry》2014,117(2):573-578
Mn4+ doped and Dy3+, Tm3+ co-doped MgAl2Si2O8-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the 2E → 4A2 transitions of Mn4+. 相似文献
76.
It is shown that mechanical vibration (acoustical oscillation) of a solid medium along the propagation of multifrequency laser radiation enables one to control the resonant absorption. There exists an optimal spectral structure of the incident field dependent on vibration amplitude as well as the number and intensity of the frequency components that provides the full resonant transparency. A mechanism of the transparency is discussed. Transparency of this kind is shown to appear also via adiabatic modulation of the atomic transition frequency by an external microwave field. 相似文献