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Summary In the original intercomparisons two of the IAEA's reference materials, milk powder A-11 and animal muscle H-4, gave unsatisfactory results, with a wide spread of values for many trace elements of interest, and subsequently the recommended values for Cu and Mn in A-11 have been questioned.In the present work, efforts to improve the status of these two materials through a co-ordinated research programme involving a small group of experienced laboratories is described. The elements chosen were As, Cd, Co, Cr, Cu, Hg, I, Mn, Mo, Ni and Pb, and the techniques used were neutron activation analysis (NAA), atomic absorption spectroscopy (AAS) in various modes, inductively coupled plasma emission spectroscopy (ICP), electrochemical methods, and also for iodine, a catalytic method.The results show a satisfactory measure of concordance for most of the elements (in marked contrast to the original results), and allow proposals to be made for revision of the recommended values. Only in the case of Ni and Pb (where NAA data are not available) is the position not fully resolved.Deceased on July 8th, 1984  相似文献   
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Following Kohn (reference 4), Schlosser and Marcus (reference 3), and Weare and Parr (reference 2), an energy functional is defined for a molecular problem which is stationary in the neighborhood of the exact solution and permits the use of trial functions that are discontinuous. The functional differs from the functional of the standard Rayleigh–Ritz method in the replacement of the usual kinetic energy operators T?(μ) with operators T?′(μ) = T?(μ) + Î(μ), where Î(μ) generates contributions from surfaces of nonsmooth behavior. If one uses the ?Ψ · ?Ψ way of writing the usual kinetic energy contributions, one must add surface integrals of the product of the average of ?Ψ and the change of ?Ψ across surfaces of discontinuity.  相似文献   
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Numerical simulation is one of primary methods in which people study the property of chaotic systems. However, there is the effect of finite precision in all processors which can cause chaos to degenerate into a periodic function or a fixed point. If it is neglected the precision of a computer processor for the binary numerical calculations, the numerical simulation results may not be accurate due to the chaotic nature of the system under study. New and more accurate methods must be found. A quantitative computable method of sequence complexity evaluation is introduced in this paper. The effect of finite precision is evaluated from the viewpoint of sequence complexity. The simulation results show that the correlation function based on information entropy can effectively reflect the complexity of pseudorandom sequences generated by a chaotic system, and it is superior to the other measure methods based on entropy. The finite calculation precision of the processor has significant effect on the complexity of chaotic binary sequences generated by the Lorenz equation. The pseudorandom binary sequences with high complexity can be generated by a chaotic system as long as the suitable computational precision and quantification algorithm are selected and behave correctly. The new methodology helps to gain insight into systems that may exist in various application domains such as secure communications and spectrum management.  相似文献   
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