Variational perturbation theory compared with computer simulations

The variational perturbation theory has been applied to describe the compressibility of a 50% mixture of helium and nitrogen at room temperature and pressures up to 1 GPa. With parameters resulting from this perturbation theory, Monte Carlo simulations have been performed on model systems for these compounds as well as for the mixture. On comparison, clear restrictions are seen for the applicability of the perturbation theory combined with the one-fluid representation of mixtures.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

The determination of the second and third virial coefficients frompVT-X data of binary systems

The compressibility factor of multicomponent systems can be obtained in terms of virial coefficients of the pure components and their binary mixtures. This paper concerns a method with which, for that purpose, the second and third virial coefficients for these binaries have been determined from experimental data. From useful data, second and third virial coefficients are obtained as a quadratic function of the temperature. The density domain for which these results are applicable is discussed. When ample data are available, results for a sample mixture can be obtained in a straightforward manner. Nevertheless, it is shown that under much less favorable conditions—sometimes even when pure-component data are lacking—fairly good results can still be obtained. In that case, the choice for an appropriate combining rule has to be considered carefully. Finally, the involvement of ternary mixture data, both obtained experimentally and predicted by the equation, is considered.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Disorder in N2 and the Mixed Solid N2–Ar: Experiment and Computer Simulations

Computer simulations and experimental measurements of the disorder in the high pressure phases of nitrogen and of the mixed solid nitrogen–argon are reported. The vibrational frequency of nitrogen has been measured in those systems with Raman spectroscopy as a function of pressure, temperature, and composition. These frequencies, together with the orientational behavior of the molecules, have also been determined by Monte Carlo simulations.     

Phase behavior of mixtures at very high pressures

The invention of the diamond anvil cell (DAC) has been an enormous stimulus to high-pressure research. This technique has only recently been used to investigate the behavior of binary systems, probably because of the extra experimental problems which arise in the study of mixtures. It will be shown that a variety of aspects of the behavior of the mixture can, nevertheless, be studied under extreme conditions. Although the first investigations were carried out only recently, some very interesting results have already been obtained. A variety of two-components systems has been studied, e.g., He-Kr, Ne-Xe, He-H₂, NH₃-H₂O, and N₂-He₂. Some of these results are discussed. Finally, a comparison is made between experimental results and theoretical calculations.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Proliferation of gemistocytic cells and glial fibrillary acidic protein (GFAP)-positive oligodendroglial cells in gliomas: a MIB-1/GFAP double labeling study

Affinity chromatography using different lytic transglycosylases as a specific ligand revealed an interaction of both murein hydrolases and murein synthases. This interaction is taken as evidence for the assemblage into a multienzyme complex that could function as a murein replicase precisely copying the given three-dimensional structure of the murein sacculus. The sacculus of the mother cell would function as a template, which is identically replicated by copying the lengths of the existing glycan strands and the pattern of crosslinkages. A hypothetical enzyme complex specifically involved in cell division and a complex specifically involved in cell elongation are presented. It is postulated that PBPs 1a and/or 1b are present in both complexes, whereas the presence of PBP2 or PBP3 defines the specificity of the murein-synthesizing machinery as being involved in either cell elongation or septation. Moreover, the proposed "holoenzyme" suprastructure could explain why the specific inhibition of PBPs 1a/1b results in bacteriolysis and why inhibition of PBP2 and PBP3 causes the well-known morphological alterations, spherical growth, and filamentation, respectively.     

The influence of grain size on the alignment of hexagonally ordered cylinders of self-assembled diblock copolymer-based supramolecules

In situ SAXS is used to investigate the shear-induced alignment of a supramolecular system consisting of a polyisoprene-b-poly(2-vinylpyridine) diblock copolymer and octyl gallate (OG), where OG is hydrogen-bonded to the vinylpyridine block of the PI-b-P2VP copolymer. Due to microphase separation, the PI-b-P2VP(OG) system self-assembles forming a domain structure of hexagonally ordered P2VP(OG) cylinders embedded in the PI matrix. The results of the alignment showed that the orientation mobility of the cylinders, lying within the (10) planes parallel to the shear plane, is strongly dependent on the size of the cylindrical domains. Subjected to large amplitude oscillatory shear for 15 min a freshly loaded sample with a small grain size structure exhibited much better alignment compared to that of a pre-aligned/squeezed sample with a considerably larger grain size where the orientation had been first partly destroyed by squeezing.     

NOx storage/reduction over lean-burn automotive catalysts

This paper shows the behavior of a Pt/Ba/γ–Al₂O₃ automotive catalyst in a fixed bed reactor during cyclic operation at lean and rich gas phase conditions at short (seconds) and long (hours) cycling times at different temperatures. Reactor exit gas phase concentrations have been measured and catalyst properties have been determined before and after selective cycling experiments. The experimental results indicate that: (i) Upon 9 h lean and 15 h rich cycling, the NO oxidation efficiency of the catalyst decreases with time while incomplete regeneration is seen, even after 15 h rich exposure with H₂. The cyclic steady state is reached after 3 lean/rich cycles, at which only 60% of the available barium is involved in the NO_x storage/reduction. (ii) The BET surface area, pore volume, and Pt dispersion decrease by approximately 40%, which may be a result of masking of Pt sites or blocking of pores of the barium clusters as BaCO₃ becomes Ba(NO₃)₂. Experiments with catalyst pellet sizes of 180 and 280 μm along with XPS measurements show that blocking of catalyst pellet pores is not taking place. (iii) When applying lean/rich cycling in the order of seconds, it appears that catalyst history and lean/rich timing affect the number of cycles required to arrive at a closed N balance. XRD results after lean exposure confirm the formation of barium nitrate in the bulk of the barium cluster.     

Enhancement Factor for Gas Absorption in a Finite Liquid Layer. Part 2: First‐ and Second‐Order Reactions in a Liquid in Plug Flow

Gas absorption accompanied by an irreversible chemical reaction of first‐order or second‐order in a liquid layer of finite thickness in plug flow has been investigated. The analytical solution to the enhancement factor has been derived for the case of a first‐order reaction, and the exact solution to the enhancement factor has been obtained via numerical simulation for the case of a second‐order reaction. The enhancement factor in both cases is presented as a function of the Fourier number and tends to deviate from the prediction of the existing enhancement factor expressions based on the penetration theory at Fourier numbers above 0.1 due to the absence of a well‐mixed bulk region in the liquid layer. Approximate enhancement factor expressions that describe the analytical and exact solutions with an accuracy of 5 % and 9 %, respectively, have been proposed.     

Intensification of convective heat transfer in a stator–rotor–stator spinning disc reactor

A stator–rotor–stator spinning disc reactor is presented, which aims at intensification of convective heat‐transfer rates for chemical conversion processes. Single phase fluid‐rotor heat‐transfer coefficients h_r are presented for rotor angular velocities rad s^?1 and volumetric throughflow rates m³s^?1. The values of h_r are independent of and increase from 0.95 kWm^?2K^?1 at ω = 0 rad s^?1 to 34 kWm^?2K^?1 at ω = 157 rad s^?1. This is a factor 2–3 higher than values achievable in passively enhanced reactor‐heat exchangers, due to the 1–2 orders of magnitude larger specific energy input achievable in the stator–rotor–stator spinning disc reactor. Moreover, as h_r is independent of , the heat‐transfer rates are independent of residence time. Together with the high mass‐transfer rates reported for rotor–stator spinning disc reactors, this makes the stator–rotor–stator spinning disc reactor a promising tool to intensify heat‐transfer rates for highly exothermal chemical reactions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2307–2318, 2015