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Kishor R. Shah Royston H. Filby Albert I. Davis 《International journal of environmental analytical chemistry》2013,93(1):63-73
Thermal neutron activation analysis, a high-resolution Ge(Li) gamma-ray spectrometer, and an IBM 360/67 digital computer were used to determine the concentration of Na, K, Sc, Cr, Mn, Fe, Co, Cu, Zn, Se, Br, Rb, Sb, Cs, and Hg in ground coffee and tea. This nondestructive multielement technique requires neither pre- nor postirradiation chemistry and eliminates problems of reagent contamination. The method is simple, precise and sensitive to 15 elements. Interferences from fast neutron (n, p) and (n, α) reactions are small and, if necessary, corrections may be applied easily. This technique can be applied to percolated tea and coffee. 相似文献
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In order to understand the dynamics of vortices on heat transfer, the unsteady flow field of tangential direction jets flowing in the annular chamber is numerically investigated by scale-adaptive simulation (SAS). The jet Reynolds number is 332,000 based on the jet’s diameter and inflow velocity for a specific geometric model. The analogy theory is used to obtain the convective heat transfer coefficient distribution on the hub surface. Spectral analysis via fast Fourier transform (FFT) is used to analyze frequency information that flows inside the chamber. The proper orthogonal decomposition (POD) method is performed on the velocity field in the chamber and the convective heat transfer coefficient on the hub surface using a snapshot method. The fast Fourier transform helps find the dominant frequency of the unsteady flow in the chamber. The time sequence of velocity fields on the radial plane shows the presence of cyclic flapping of the jet. The proper orthogonal decomposition analysis indicates that the unsteady periodic flow phenomenon in the chamber and unsteady heat transfer on the hub surface are mainly related to the dynamics of the counter-rotating vortices caused by the jet. 相似文献
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V. I. Fabrikant 《Archive of Applied Mechanics (Ingenieur Archiv)》2001,71(6-7):371-388
Summary The following mixed boundary-value problem for a transversely isotropic elastic half-space is considered. Arbitrary tangential
displacements are prescribed at the exterior of a circle, while the interior of the circle is free of tangential stress, and
the normal stress vanishes all over the boundary. The governing integral equation is solved exactly, in closed form, and in
terms of elementary functions. The method of continuation of solutions previously published by the author has been used here.
Several examples are considered. No similar results has been reported before, even in the case of an isotropic body.
Received 8 May 2000; accepted for publication 20 July 2000 相似文献
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In this study the tangential partial slip problems in Hertzian contact regions are treated by a numerical technique. The tangential
loading may include tangential forces in the contact plane and a twisting moment normal to the contact plane. The Coulomb’s
law of friction and the property that the direction of friction must oppose the relative motion lead to nonlinear equations.
The Newton-Raphson method is utilized to solve these nonlinear equations. Numerical results for tangential tractions and sizes
of stick and slip zones may be determined, and they agree with existing analytical results for circular contacts. 相似文献
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Daniel Girela M. Auxiliadora Márquez 《Journal of Mathematical Analysis and Applications》2005,309(2):534-543
A well-known theorem of H.S. Shapiro and A.L. Shields implies that if f?0 is a function which belongs to the Bergman space Ap (0<p<∞) and {zk} is a sequence of zeros of f which is contained in a Stolz angle, then {zk} satisfies the Blaschke condition. In this paper we improve this result. We consider a large class of regions contained in the unit disc D which touch ∂D at a point ξ tangentially and we prove that the mentioned result remains true if we substitute a Stolz angle by any of these regions of tangential approach. 相似文献
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Wang Han Arne Scholtissek Christian Hasse 《Proceedings of the Combustion Institute》2019,37(2):1767-1774
For non-premixed combustion, the steady laminar flamelet model (SLFM) and flamelet/progress variable approach (FPVA) are two popular methods for tabulating flamelet manifolds. Even if the two methods are used to tabulate and parameterize the same flamelet database, their results sometimes differ in the subsequent simulation. In this work, a novel perspective is provided to assess the performance of the SLFM and FPVA. Both approaches are compared with respect to their capabilities to capture tangential diffusion (TD) of the thermochemical state variables along iso-surfaces of mixture fraction. The relevance of TD effects is identified using generalized flamelet equations and regimes by comparing flamelet solutions with and without TD terms to a FTC (full transport and chemistry) solution of a well-known non-premixed coflow flame. It is found that TD effects can play an important role in entire mixture fraction space, even in the classical flamelet regime. This suggests that the ability to characterize TD effects is an important performance indicator for tabulation strategies. Thereafter, an a priori analysis is conducted comparing the results from the FPVA and SLFM (using the same flamelet database) with the FTC results. The results show that the FPVA is able to more accurately describe the thermochemical state and the flame structure than the SLFM. For a more detailed assessment of the two tabulation strategies, the TD terms reconstructed from the FPVA and SLFM are compared to those from the FTC results. It is found that the FPVA can capture a significant portion of TD effects, while the SLFM can hardly characterize TD effects. This particular capability allows the FPVA to describe chemistry-transport interaction and flame structure more accurately than the SLFM. 相似文献
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Vijayakumar Sinnathurai John H. Curran Reginald Hammah 《Mechanics Research Communications》2008,35(4):237-245
It is shown that the anomaly associated with the incorrect evaluation of tangential stresses in the displacement discontinuity (DD) method, commonly used to solve crack problems, is related to the order of singularity of the fundamental solutions of linear elasticity. It is established here that a minimum of linear variation of the shear DD distribution is needed to obtain the correct tangential stress jump across a crack. Alternatively, a correction term (‘patch’) that improves tangential stresses is derived. It is also shown that need for higher functionality is a fundamental requirement rather than a convenient artifice for obtaining better accuracy. 相似文献