Group contributions to activity coefficients from the hard sphere expansion corresponding states theory

A new method has been developed for predicting liquid activity coefficients in ternary mixtures from group contributions. In this method, activity coefficients are obtained from the excess Gibbs free energy of mixing at constant temperature and pressure. In calculating this excess function, the constituent and mixture Gibbs free energies are each represented by an expansion about a pure reference fluid in powers of ratios of hard-sphere diameters and molecular attraction parameters. When the pure component differs from the reference by a single structural group, these ratios represent, respectively, the size contribution and the attraction contribution of this group to the thermodynamic property of the pure fluid. Contributions of intermolecular repulsion to the excess Gibbs free energy are calculated directly from hard-sphere equations of state for the mixture and pure components. The effect of polar contributions calculated by a Padé approximant is also examined. Results indicate that the method developed from the hard-sphere expansion corresponding-states theory is useful for predicting activity coefficients in ternary mixtures when unlike-pair interaction parameters are fitted to binary activity coefficient data. Furthermore, the method shows promise in providing a theoretical basis for applying group contributions to activity coefficients.Nomenclature A Residual Helmholtz free energy - C _p Constant-pressure heat capacity - H _vap Heat of vaporization - P ^s Saturated vapor pressure - R Gas constant - T Temperature - U ^HS Hard-sphere internal energy - V _c Critical volume - V ^L Liquid volume - x Dimensionless residual thermodynamic property - Z Compressibility factor - d Center-to-center distance between two touching molecules - k Boltzmann constant - n Moles - x Liquid mole fraction - y Vapor mole fraction - Volume expansivity - Liquid activity coefficient - Minimum molecular attraction potential - Isothermal compressibility - Permanent dipole moment - 3.14159... - Density - Fugacity coefficient Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Stacking graphic elements to avoid over-plotting

An ongoing challenge for information visualization is how to deal with over-plotting forced by ties or the relatively limited visual field of display devices. A popular solution is to represent local data density with area (bubble plots, treemaps), color (heatmaps), or aggregation (histograms, kernel densities, pixel displays). All of these methods have at least one of three deficiencies:1) magnitude judgments are biased because area and color have convex downward perceptual functions, 2) area, hue, and brightness have relatively restricted ranges of perceptual intensity compared to length representations, and/or 3) it is difficult to brush or link to individual cases when viewing aggregations. In this paper, we introduce a new technique for visualizing and interacting with datasets that preserves density information by stacking overlapping cases. The overlapping data can be points or lines or other geometric elements, depending on the type of plot. We show real-dataset applications of this stacking paradigm and compare them to other techniques that deal with over-plotting in high-dimensional displays.     

High Order Schemes for Resolving Waves: Number of Points per Wavelength

For energetic flows there are many advantages of high order schemes over low order schemes. Here we examine a previously unknown advantage. It is commonly thought that the number of points per wavelength in order to obtain a given error in a numerical approximation depends only on runtime and the order of the approximation. Using truncation error arguments and examples we will show that it is not a constant and depends also on the wavenumber. This dependence on the numerical order and wavenumber strongly favors high order schemes for use in flows which have significant energy in the high modes such at Rayleigh–Taylor and Richtmyer–Meshkov instabilities.     

Extending the Fatigue Life of Riveted Coped Stringer Connections

Fatigue cracking occurs at the copes of stringer–floorbeam connections of older, riveted steel bridges. Some cracks are quite long and raise serious questions regarding the remaining fatigue life of the subject bridges. Damage limitation methods (DLMs) have been used to increase the fatigue life of these stringers, but the effectiveness of the DLMs for these riveted connections had never been evaluated by tests. Therefore, tests were conducted to evaluate the fatigue life of coped, riveted stringer–floorbeam connections, and the effectiveness of DLMs. Fatigue cracks in the coped stringer–floorbeam connection were initially developed to establish crack initiation requirements and the rate and extent of crack growth. Once a significant crack was noted, one of several DLMs was applied, and the specimens were retested to determine the effectiveness of the DLM in controlling cracking. These DLMs included the drilled hole, the inserted bolt and the removed rivet methods. The relative effectiveness of the methods is described, and a design procedure is proposed for improving their performance.     

Mechanical-thermal noise in MEMS gyroscopes

We derive expressions for the effect of mechanical thermal noise on a vibrational microelectromechanical system gyroscope, including the angle of random walk, the noise equivalent rotation rate, and the spectral density of the noise component of the rate measurement. We explicitly calculate and compare the output signal due to rotation and the output due to noise. We avoid several ambiguities in the literature concerning bandwidth and correctly observe a factor of two reduction in noise power due to synchronous demodulation. We use stochastic averaging to obtain an approximate "slow" system that clarifies the effect of thermal noise and shows the effect of frequency mismatch between the drive and sense axes. We compute the noise equivalent rate for both open-loop and force-to-rebalance operation of the gyroscope.     

Ribonuclease A variants with potent cytotoxic activity

Select members of the bovine pancreatic ribonuclease A (RNase A) superfamily are potent cytotoxins. These cytotoxic ribonucleases enter the cytosol, where they degrade cellular RNA and cause cell death. Ribonuclease inhibitor (RI), a cytosolic protein, binds to members of the RNase A superfamily with inhibition constants that span 10 orders of magnitude. Here, we show that the affinity of a ribonuclease for RI plays an integral role in defining the potency of a cytotoxic ribonuclease. RNase A is not cytotoxic and binds RI with high affinity. Onconase, a cytotoxic RNase A homolog, binds RI with low affinity. To disrupt the RI-RNase A interaction, three RNase A residues (Asp-38, Gly-88, and Ala-109) that form multiple contacts with RI were replaced with arginine. Replacing Asp-38 and Ala-109 with an arginine residue has no effect on the RI-RNase interaction. In addition, these variants are not cytotoxic. In contrast, replacing Gly-88 with an arginine residue yields a ribonuclease (G88R RNase A) that retains catalytic activity in the presence of RI and is cytotoxic to a transformed cell line. Replacing Gly-88 with aspartate also yields a ribonuclease (G88D RNase A) with a decreased affinity for RI and cytotoxic activity. The cytotoxic potency of onconase, G88R RNase A, and G88D RNase A correlate with RI evasion. We conclude that ribonucleases that retain catalytic activity in the presence of RI are cytotoxins. This finding portends the development of a class of chemotherapeutic agents based on pancreatic ribonucleases.     

CONCENTRATION POLARIZATION ANALYSIS AT THE ENTRANCE REGION OF A FLAT SHEET PERVAPORATION MODULE FOR VOC REMOVAL

Concentration polarization is a phenomenon that is inherent in all membrane separation processes, which is difficult if not impossible to measure experimentally. Concentration polarization in a pervaporation module causes flux decline and is therefore an important issue in predicting the performance of the membrane unit for evaluation and optimization. Short-form (small L/D ratio) membrane configurations, commonly used for membrane evaluations or certain material separations, compound the complexity of process modeling that addresses concentration polarization since a substantial portion of the membrane flow channel would be considered as an “entrance region” based on the flow profile that is not fully developed. This article employed the classic boundary layer theory, combined with mass transfer phenomena in a pervaporation process that is used in volatile organic compound (VOC) removal from contaminated water sources, to theoretically analyze the concentration polarization severity in the entrance region of a flat sheet membrane module.     

Shape estimation of a circular antenna from observations on the boundary

A smoothing algorithm for estimating the shape of a circular antenna from boundary observations is described. We consider a homogenized static antenna model, consisting of a single partial differential equation with mixed boundary conditions. An exact expression is derived for the smoother, and a suitable approximation is calculated. An FFT based implementation is found to be computationally efficient. Simulation results for 8, 16, 32 and 64 sensors are given, indicating a point of diminishing returns in adding more sensors.     

Sterol metabolism: XII. 26-hydroxycholesterol in commercial cholesterol

Commercial cholesterol of bovine brain and spinal cord origin has been care-fully examined for its 24- and 26-hydroxycholesterol content. By alternate adsorption chromatography and chromatography on Sephadex LH-20 26-hydroxycholesterol was isolated from this course in 15 μg/g amounts, whereas 24-hydroxycholesterol was not observed. Paper XI of this series: J.E. van Lier and L.L. Smith, Steroids 15:485–503 (1970).