Applied Biochemistry and Biotechnology - Kinetic and mass transport parameters were estimated for maltotriose hydrolysis using glucoamylase immobilized on macroporous silica and wrapped in pectin... 相似文献
The effective elastic properties of a polycrystalline material depend on the single crystal elastic constants of the crystallites
comprising the polycrystal and on the manner in which the crystallites are arranged. In this paper we apply the techniques
of homogenization to put the problem of determining effective elastic constants in a precise mathematical framework that permits
us to derive an expression for the effective elasticity tensor. We also study how the homogenized elasticity tensor changes
as the probability characterizing the ensemble changes. Under the assumption that the field of orientations of the crystallographic
axes of the crystallites is an independent random field, we show that our theory is compatible with the formulation used in
texture analysis. In particular, we are able to prove that the physical assumption made by [10] in his study of weakly-textured polycrystals holds true.
In addition, we establish some elementary bounds on the material constants that characterize the effective elasticity tensor
of weakly-textured orthorhombic aggregates of cubic crystallites.
Accepted: (June 15, 1999) 相似文献
The activity coefficients of K3[Co(CN)6], Mg3[Co(CN)6]2, and Ca3[Co(CN)6]2,are examined. The results highlight close similarity with the correspondinghexacyanoferrate (III) salts. On dilution, K3[Co(CN)6], like K3[Fe(CN)6], approachesthe limiting law from the upper side, while Mg3[Co(CN)6]2 and Ca3[Co(CN)6]2tend to the limiting law from the opposite side, like Mg3[Fe(CN)6]2,Ca3[Fe(CN)6]2, Sr3[Fe(CN)6]2, and Ba3[Fe(CN)6]2. Both kinds of behavior agreewith theory for a model of hard spheres bearing electric charges +1 and –3 or+2 and –3, respectively. The paramater values of the Pitzer equation for activityand osmotic coefficients are reported. 相似文献
In this work we examine first the flow field of a confined jet produced by a turbulent flow in a long cylindrical pipe issuing
in an abrupt angle diffuser. Second, we examine the dispersion of inertial micro-particles entrained by the turbulent flow.
Specifically, we examine how the particle dispersion field evolves in the multiscale flow generated by the interactions between
the large-scale structures, which are geometry dependent, with the smaller turbulent scales issued by the pipe which are advected
downstream. We use Large-Eddy-Simulation (LES) for the flow field and Lagrangian tracking for particle dispersion. The complex
shape of the domain is modelled using the immersed-boundaries method. Fully developed turbulence inlet conditions are derived
from an independent LES of a spatially periodic cylindrical pipe flow. The flow field is analyzed in terms of local velocity
signals to determine spatial coherence and decay rate of the coherent K–H vortices and to make quantitative comparisons with
experimental data on free jets. Particle dispersion is analyzed in terms of statistical quantities and also with reference
to the dynamics of the coherent structures. Results show that the particle dynamics is initially dominated by the Kelvin–Helmholtz
(K–H) rolls which form at the expansion and only eventually by the advected smaller turbulence scales. 相似文献
This paper presents a hybrid stress approach for the analysis of laminated composite plates. The plate mechanical model is based on the so called First-order Shear Deformation Theory, rationally deduced from the parent three-dimensional theory. Within this framework, a new quadrilateral four-node finite element is developed from a hybrid stress formulation involving, as primary variables, compatible displacements and elementwise equilibrated stress resultants. The element is designed to be simple, stable and locking-free. The displacement interpolation is enhanced by linking the transverse displacement to the nodal rotations and a suitable approximation for stress resultants is selected, ruled by the minimum number of parameters. The transverse stresses through the laminate thickness are reconstructed a posteriori by simply using three-dimensional equilibrium. To improve the results, the stress resultants entering the reconstruction process are first recovered using a superconvergent patch-based procedure called Recovery by Compatibility in Patches, that is properly extended here for laminated plates. This preliminary recovery is very efficient from the computational point of view and generally useful either to accurately evaluate the stress resultants or to estimate the discretization error. Indeed, in the present context, it plays also a key role in effectively predicting the shear stress profiles, since it guarantees the global convergence of the whole reconstruction strategy, that does not need any correction to accommodate equilibrium defects. Actually, this strategy can be adopted together with any plate finite element. Numerical testing demonstrates the excellent performance of both the finite element and the reconstruction strategy. 相似文献
The local flexibility introduced by cracks changes the dynamic behavior of the structure and, by examining this change, crack position and magnitude can be identified. In order to model the structure for FEM analysis, a special finite element for a cracked Timoshenko beam is developed. Shape functions for rotational and translational displacements are used to obtain the consistent mass matrix for the cracked beam element. Effect of the crack on the stiffness matrix and consistent mass matrix is investigated. Proposed is a procedure for identifying cracks in structures using modal test data. 相似文献
Metallic nanoparticles are known to enhance nonlinear optical processes due to a local enhancement of the optical field. This strategy has been proposed to enhance downconversion in thin film solar cells, but has various disadvantages, among which is the fact that the enhancement occurs only in a tiny volume close to the particles. We report on a very different physical mechanism that can lead to significant downconversion enhancement, namely, that of resonant light scattering, and which is a large volume effect. We show that only a tiny amount of resonantly scattering metallic (aluminum) nanoparticles is enough to create a significant enhancement of the fluorescence of dye molecules in the visible wavelength range. The strategy can be applied in general to increase the emission of UV-absorbing constituents, and is of particular use for solar energy. 相似文献
Summary: The range of validity of two popular versions of the nitroxide quasi‐equilibrium (NQE) approximation used in the theory of kinetics of alkoxyamine mediated styrene polymerization, are systematically tested by simulation comparing the approximate and exact solutions of the equations describing the system. The validity of the different versions of the NQE approximation is analyzed in terms of the relative magnitude of (dN/dt)/(dP/dt). The approximation with a rigorous NQE, kc[P][N] = kd[P N], where P, N and P N are living, nitroxide radicals and dormant species respectively, with kinetic constants kc and kd, is found valid only for small values of the equilibrium constant K (10−11–10−12 mol · L−1) and its validity is found to depend strongly of the value of K. On the other hand, the relaxed NQE approximation of Fischer and Fukuda, kc[P][N] = kd[P N]0 was found to be remarkably good up to values of K around 10−8 mol · L−1. This upper bound is numerically found to be 2–3 orders of magnitude smaller than the theoretical one given by Fischer. The relaxed NQE is a better one due to the fact that it never completely neglects dN/dt. It is found that the difference between these approximations lies essentially in the number of significant figures taken for the approximation; still this subtle difference results in dramatic changes in the predicted course of the reaction. Some results confirm previous findings, but a deeper understanding of the physico‐chemical phenomena and their mathematical representation and another viewpoint of the theory is offered. Additionally, experiments and simulations indicate that polymerization rate data alone are not reliable to estimate the value of K, as recently suggested.
Validity of the rigorous nitroxide quasi‐equilibrium assumption as a function of the nitroxide equilibrium constant. 相似文献