A correlation for yield stress fluid flow through packed beds

Relatively few correlations are available for non-Newtonian fluid flows through packed beds, even though such fluids are frequently used in industry. In this paper, a correlation is presented for yield stress fluid flow through packed beds. The correlation is developed by introducing the yield stress model in place of the Newtonian model used in deriving Erguns equation. The resulting model has three parameters that are functions of the geometry and roughness of the particle surfaces. Two of the parameters can be deduced in the limit as the yield stress becomes negligible and the model reduces to Erguns equation for Newtonian fluids. The third model parameter is determined from experimental data. The correlation relates a defined friction factor to the dimensionless Reynolds and Hedstrom numbers and can be used to predict pressure drop for flow of a yield stress fluid through a packed bed of spherical particles. Conditions for flow or no-flow are also determined in the correlation. Comparison of model calculations, between a Newtonian and a yield stress fluid for flow penetration into a packed bed of spheres, shows the yield stress fluid initially performs similar to the Newtonian fluid, at large Reynolds numbers. At lower Reynolds numbers the yield stress effect becomes important and the flow rate significantly decreases when compared to the Newtonian fluid.     

Fluctuations of multiplicities in rapidity windows in sulphur-sulphur collisions at 200A GeV

Multiplicity distributions and their second moments fornegatively charged particles produced in³²S-S central and minimum bias interactions at 200A GeV are studied in various rapidity intervals. Fritiof and Venus models mostly describe the dependence of second moments on rapidity intervals in minimum bias interactions, but not in central collisions. For central collisions the behaviour of second moments might indicate enhanced multiplicity fluctuations.     

Conformational analysis of gossypol and its derivatives by molecular mechanics

Conformations and inversion pathways leading to racemization of all the tautomers of gossypol, gossypolone, anhydrogossypol, and a diethylamine Schiff's base of gossypol were investigated with MM3(2000). All forms have hindered rotation because of clashes between the methyl carbon atom and oxygen-containing moieties ortho to the bond linking the two naphthalene rings. Inversion energies generally agree with available experimental data. Gossypol preferentially inverts in its dihemiacetal tautomeric form through the cis pathway (where similar groups clash). Gossypolone inverts more easily than gossypol, and preferentially through the trans pathway (where dissimilar groups clash) when one of its outer rings has an enol-keto group and the other has an aldehyde group. Anhydrogossypol racemizes through the cis pathway. The bridge bond and the ortho exo-cyclic bonds in all the structures bend from planarity, and the inner naphthalene rings pucker to accommodate the inversion. For gossypol, the transition is achieved through greater bending of the exo-cyclic bonds (up to 12°) and less distortion of the inner benzyl rings (q≤0.34 Å), (up to 12.7°) . For gossypolone the transition occurs with greater distortion of the inner benzyl rings (q≤0.63 Å) and less out-of-plane bending (up to 8.4°). By isolating individual clashes, their contribution to the overall barrier can be analyzed, as shown for the dialdehyde tautomer of gossypol.     

Intensity perception. XII. Effect of presentation probability on absolute identification

Identification experiments using 13 tone-pulse stimuli (1000 Hz, 500 ms) spaced by equal decibel increments from 42 to 90 dB SPL were conducted under three conditions: all intensities equally likely (denoted Q), the middle intensity presented on roughly 1/3 of the trials (M), and each of the extreme intensities presented on roughly 1/5 of the trials (E). Experiments were performed both with and without feedback, and results were analyzed in terms of sensitivity and bias. Similar results were obtained with and without feedback: listeners generally shifted biases in the M and E conditions relative to the Q condition to increase percent-correct scores, but there were only minor changes in sensitivity from condition to condition. However, sensitivities were generally higher and biases more optimal when feedback was available. The results on sensitivity are consistent with those associated with payoff variation [Lippmann et al., J. Acoust. Soc. Am. 59, 129-134 (1976)], but are inconsistent with those reported for presentation probability variation in tone frequency identification [Cuddy et al., J. Exp. Psychol. 100, 218-220 (1973)]. In an auxilliary experiment concerned with tone frequency identification, results consistent with those obtained for intensity, but inconsistent with those reported by Cuddy et al., were obtained.     

Raman scattering from sodium and silver in β-alumina

Raman scattering is observed from the vibrations of the mobile sodium and silver ions in β-alumina between 4.2 and 900°K. The frequency response is Lorentzian at all temperatures above 300°K with little change in frequencies and damping rates. It is concluded that diffusive conduction with a well-defined attempt frequency predominates up to 900°K.     

Gaussian core model phase diagram and pair correlations in high Euclidean dimensions

The physical properties of a classical many-particle system with interactions given by a repulsive Gaussian pair potential are extended to arbitrarily high Euclidean dimensions. The goals of this paper are to characterize the behavior of the pair correlation function g(2) in various density regimes and to understand the phase properties of the Gaussian core model (GCM) as parametrized by dimension d. To this end, we explore the fluid (dilute and dense) and crystalline solid phases. For the dilute regime of the fluid phase, a cluster expansion of g(2) in reciprocal temperature beta is presented, the coefficients of which may be evaluated analytically due to the nature of the Gaussian potential. We present preliminary results concerning the convergence properties of this expansion. The analytical cluster expansion is related to numerical approximations for g(2) in the dense fluid regime by utilizing hypernetted chain, Percus-Yevick, and mean-field closures to the Ornstein-Zernike equation. Based on the results of these comparisons, we provide evidence in support of a decorrelation principle for the GCM in high Euclidean dimensions. In the solid phase, we consider the behavior of the freezing temperature T(f)(rho) in the limit rho-->+infinity and show T(f)(rho)-->0 in this limit for any d via a collective coordinate argument. Duality relations with respect to the energies of a lattice and its dual are then discussed, and these relations aid in the Maxwell double-tangent construction of phase coexistence regions between dual lattices based on lattice summation energies. The results from this analysis are used to draw conclusions about the ground-state structures of the GCM for a given dimension.     

Metal-free catalytic hydrogenation of polar substrates by frustrated Lewis pairs

In 2006, our group reported the first metal-free systems that reversibly activate hydrogen. This finding was extended to the discovery of "frustrated Lewis pair" (FLP) catalysts for hydrogenation. It is this catalysis that is the focal point of this article. The development and applications of such FLP hydrogenation catalysts are reviewed, and some previously unpublished data are reported. The scope of the substrates is expanded. Optimal conditions and functional group tolerance are considered and applied to targets of potential commercial significance. Recent developments in asymmetric FLP hydrogenations are also reviewed. The future of FLP hydrogenation catalysts is considered.     

A facility neighborhood search heuristic for capacitated facility location with single-source constraints and flexible demand

We consider a generalization of the well-known capacitated facility location problem with single source constraints in which customer demand contains a flexible dimension. This work focuses on providing fast and practically implementable optimization-based heuristic solution methods for very large scale problem instances. We offer a unique approach that utilizes a high-quality efficient heuristic within a neighborhood search to address the combined assignment and fixed-charge structure of the underlying optimization problem. We also study the potential benefits of combining our approach with a so-called very large-scale neighborhood search (VLSN) method. As our computational test results indicate, our work offers an attractive solution approach that can be tailored to successfully solve a broad class of problem instances for facility location and similar fixed-charge problems.