Wetting properties of the multiscaled nanostructured polymer and metallic superhydrophobic surfaces

A superhydrophobic surface is produced from industrial grade polymer materials. The surface comprises partly disordered triple-scaled arrays of polyvinylidene fluoride (PVDF) globules. An inherently superhydrophobic metallic surface is produced with polymer template. The mathematical model based on the Cassie-Baxter hypothesis of air trapping under a water drop is built, which gives the apparent contact angle on the manifold-scaled interface. The presence of several scales itself is not a sufficient condition of hydrophobicity of inherently wettable surfaces. The geometrical features favoring the increase of the vapor-water interface fraction are necessary for this phenomenon.     

Methods for scaling to doubly stochastic form

New methods for scaling square, nonnegative matrices to doubly stochastic form are described. A generalized version of the convergence theorem of Sinkhorn and Knopp (1967) is proved and applied to show convergence for these new methods. Tests indicate that one of the new methods has significantly better average and worst-case behavior than the Sinkhorn-Knopp method; for one of the 3 × 3 examples of Marshall and Olkin (1968), SK requires 130 times as many operations as the new algorithm to achieve row and column sums 1±10^-5.     

Broad-line NMR of aromatic polyamides

Broad-line NMR spectra have been obtained at 90 MHz in the temperature region 140–530°K for four aromatic polyamides: poly(1,3-phenylene isophthalamide), poly(1,4-phenylene terephthalamide), poly(4,4,-diphenylene terephthalamide), and poly(4,4,-diphenylene isophthalamide). For the latter three materials, a broad-line narrowing process occurs in the 210–370°K region. At temperatures above 340°K a complex line shape is observed for all samples. Possible causes of these processes are discussed, and comparison made with dynamic mechanical results.     

Computerized technique in organic microelemental analysis: Part II. Automatic determination of sulfur in organic compounds

Described is the automatic and computerized rapid microanalytical determination of sulfur in organic and organometallic compounds. The procedure consists of the combustion of the compound in an empty tube, transfer of combustion products to the titration vessel by automatic wash, and, finally, colorostatic titration of sulfuric acid with Ba(ClO₄)₂ against dimethylsulfonazo III.The entire analysis and preparation of the equipment for the next determination are programmed in time of the 6-min cycle.The analyzer is interfaced to the departmental real-time time-sharing computer, along with electronic microbalances and other analyzers, as a part of the microanalytical laboratory computer service.Results of the analyses are reported on CR terminals and are also stored on the magnetic disc for further processing.     

Two-phase pressure drop in multiple thick- and thin-orifice plates

Two-phase flow pressure changes through singularities such as sudden expansion and sudden contraction of thick- and thin-orifice plates were modeled. The modeling was based on the reversible and irreversible losses through contractions and expansions. The volume-averaged momentum equation and the reversible mechanical energy equation were used to evaluate the irreversibilities. Local slip ratios, which were necessary for the prediction of pressure drop through these singularities, were correlated from a large number of experimental data. To check the validity of the analytical predictions, an experimental test section was designed, and experiments were performed to produce benchmark pressure-drop data for thin- and thick-plate orifices. The working fluid used for these experiments was R-113. The predictive methods developed agree well with the experiments by the authors and with a wide range of two-phase flow test results obtained by others for steam-water systems. A parametric study shows the relative importance of geometry and of the flow variables such as quality, liquid-to-vapor density, and viscosity ratios on the pressure drop multipliers conventionally used in two-phase flows.     

P450 CYP17A1 Variant with a Disordered Proton Shuttle Assembly Retains Peroxo-Mediated Lyase Efficiency

Human cytochrome P450 CYP17A1 first catalyzes hydroxylation at the C17 position of either pregnenolone (PREG) or progesterone (PROG), and a subsequent C₁₇−C₂₀ bond scission to produce dehydroepiandrosterone (DHEA) or androstenedione (AD). In the T306A mutant, replacement of the Threonine 306 alcohol functionality, essential for efficient proton delivery in the hydroxylase reaction, has only a small effect on the lyase activity. In this work, resonance Raman spectroscopy is employed to provide crucial structural insight, confirming that this mutant, with its disordered proton shuttle, fails to generate essential hydroxylase pathway intermediates, accounting for the loss in hydroxylase efficiency. Significantly, a corresponding spectroscopic study with the susceptible lyase substrate, 17-OH PREG, not only reveals an initially trapped peroxo-iron intermediate experiencing an H-bond interaction of the 17-OH group with the proximal oxygen of the Fe-O_p-O_t fragment, facilitating peroxo- attack on the C₂₀ carbon, but also unequivocally shows the presence of the subsequent hemiketal intermediate of the lyase reaction.     

Sequential Wald Test Employing a Constrained Filter Bank: Application to Spacecraft Conjunctions

A binary Wald sequential probability ratio test that uses the residuals of two norm-inequality-constrained Kalman filters for its likelihood ratio is employed for a class of compound hypothesis tests on non-stationary systems. The hypotheses concern an inequality constraint on the norm of some elements of the system state. Each of the two constrained Kalman filters minimizes the summed squares of its estimation errors subject to one or the other direction of the inequality constraint. This test is applied to the problem of spacecraft conjunction assessment, wherein the constraint concerns the close approach distance between a spacecraft and another space object. The outcome of the test can inform decisions concerning risk mitigation maneuvers by an active spacecraft.

     

Bead-spring models of entangled polymer melts: Comparison of hard-core and soft-core potentials

Two bead-spring models of flexible chains for generic coarse graining of entangled polymer melts, the excluded volume Kremer–Grest (KG) model and the modified segmental repulsive potential (mSRP) combined with a weakly repulsive potential, are compared. For chains containing an equivalent number of entanglements, we compare the chain characteristics of the KG and mSRP polymer models by determining the ratios of the entanglement lengths , the required total number of particles to capture comparable entanglement phenomena , and the time scaling ratios τ^mSRP/τ^KG. Our findings show that systems using the mSRP polymer model require half the number of particles and relax four times faster compared to the KG polymer model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012