Search Results
Abstract
The authors continue their considerations concerning the validity of the steady-state approximation in non-isothermal kinetics. A sequence of two first-order consecutive reactions with an active intermediate was subjected to kinetic analysis by numerical solution of the corresponding differential kinetic equations for a number of particular cases. The results demonstrated that the rate of change of concentration of the active intermediate is negligibly small if the assumption made in the isothermal case is also accepted for the non-isothermal case, i.e. k 2(T(t))>> k 1(T(t)).
Abstract
The complexities involved in dealing with the requirements of trace element research studies in the life sciences demand comprehensive planning of the investigations and use of a variety of techniques. It also requires a combination of biological insight and analytical awareness on the part of the investigators in order to obtain valid samples for analysis. Thus, the generation of meaningful conclusions from elemental composition studies on biological systems is a strictly multidisciplinary task, an approach that is vital for the overall success of the investigations. In addition, new initiatives are needed to produce multipurpose biological reference materials to cope with the growing demands of this multifaceted area of research. These aspects are discussed.
Abstract
We have examined the working diameter of capillary columns with diameter of 5, 7, 10 and 20 mm. These modified capillary columns were carefully filled with local Taiwan laterite (LTL). The porosity and density of these packed columns was 0.51±0.02 g/g and 1.27±0.05 g/cm3, respectively. The diffusion experiments were then carried out in synthetic groundwater with Cs loading of 0.1mM at room temperature. Experimental results have shown that the diffusion profiles of modified capillary columns fit Fick’s second law very well. This result revealed that the working diameter of a capillary column can be expanded to at least to 20 mm without affecting the validity of the derived diffusion coefficients. Among these columns, the ones with 5 mm diameter show the most consistent results of the derived K d, apparent and effective diffusion coefficients. Although the derived distribution and effective diffusion coefficients slightly decrease as the diameter of these columns increases due to the increase of the solid/liquid ratio. These values are still informative of the Cs diffusion in local Taiwan laterite. Moreover, our results clearly demonstrate the potential of using “modified capillary method” to study the diffusion behaviors of concerned radionuclide because columns with large diameter enable the filling with more versatile geological substances.
Abstract
The paper investigates the validity of steady-state approximation for the case of constant rate thermal analysis experiments. It is shown that the approximation holds for the experiments run with a controlled rate of either the decomposition of the compound, or the production of gas.
Abstract
X-ray spectrometric technique has been described to determine the X-ray mass attenuation coefficient, μ/ρ, of X-rays employing HPGe X-ray detector and radioactive sources. The photon intensity is measured by gating the channel of the spectrometer at FWHM/photo peak. Using the technique the “best value” values of μ/ρ were obtained for those thicknesses which lie in the transmission (T) range 0.5 ≥ T ≥ 0.02. Total attenuation cross sections for other elements and lead compounds were measured at photon energies from 17 to 88 keV to study the Bragg’s additivity law near the absorption edge of the lead. The measured values of mass attenuation coefficient values are compared with theoretical values obtained using Winxcom (programme). This study suggests that measured mass attenuation coefficient values at and near absorption edges differ from the theoretical value by about 17–23%.
Abstract
The determination of fluorine in the fluorides of 31 elements by prompt analysis using the reactions (α, p0), (α, α1), (α, n1γ) and (α, p1γ) on19F was carried out in a search for discrepancies that could point to molecular effects in range corrections. Data for each reaction were normalised and normalisation factors were compared. The results for each compound were in good agreement, but intercomparison showed that the accuracy of stopping power data and the applicability of Bragg’s Law were acceptable within ±8%.
Abstract
Using 8 modifications of recently developed flexible water potentials, zeropoint energy differences between the isomeric water-dimer isotopomers differing in the hydrogen isotope involved in the hydrogen bond have been evaluated. In all the 18 possible pairs, the species bound through the heavier isotope is always lower in the energy term.
In defense of thermodynamics
Comment on “Concepts against mathematics: self-inconsistency in thermodynamic evaluations”
by this notation is essential for correct mathematical derivations. Sections “ Is the value of ambiguous? ,” “ Does thermodynamics predict that ∂ H / ∂ T equals both V and 0? ,” and “ Does a valid mathematical derivation predict that C
Testing the equations Testing the validity of the derived equations Equations 19 – 21 are related with simple transformations. To demonstrate the validity of all these equations, it is enough to test the linear relationship
Dielectric-differential thermal analysis
Part V: The role of cationic conduction
A quantitative relation is given for the temperature function of the output voltage is thermodielectric analysis. Results obtained with zeolites show the validity of the equation.
