Numerical Prediction of Two-Phase Flow through a Tube Bundle Based on Reduced-Order Model and a Void Fraction Correlation

Predicting the void fraction of a two-phase flow outside of tubes is essential to evaluate the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture properties and affects two-phase mixture velocity, which enable evaluating the pressure drop of the system. The two-fluid model for the numerical simulation of two-phase flows requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. Therefore, the mixture model, for which it is easier to implement suitable correlations for tube bundles, is used. Indeed, by expressing the relative velocity as a function of slip, the void fraction model of Feenstra et al. and Hibiki et al. developed for upward cross-flow through horizontal tube bundles is introduced and compared. With the method suggested in this paper, the physical phenomena that occur in tube bundles are taken into consideration. Moreover, the tube bundle is modelled using a porous media approach where the Darcy–Forchheimer term is usually defined by correlations found in the literature. However, for some tube bundle geometries, these correlations are not available. The second goal of the paper is to quickly compute, in quasi-real-time, this term by a non-intrusive parametric reduced model based on Proper Orthogonal Decomposition. This method, named Bi-CITSGM (Bi-Calibrated Interpolation on the Tangent Subspace of the Grassmann Manifold), consists in interpolating the spatial and temporal bases by ITSGM (Interpolation on the Tangent Subspace of the Grassmann Manifold) in order to define the solution for a new parameter. The two developed methods are validated based on the experimental results obtained by Dowlati et al. for a two-phase cross-flow through a horizontal tube bundle.     

Synthesis with immobilized enzyme of the most important sialic acid.

Starting from a crude mixture of N-acetylmannosamine and N-acetylglucosamine, N-acetylneuraminic acid has been easily synthesized on 2.8 millimoles scale, with one immobilized enzyme.     

Isolation and structure (x-ray analysis) of karinolide,a new quassinoid from Simaba Multiflora

Karinolide $\text{1}$ is a structurally novel C₂₀ quassinoid isolated from the French Guyanan Simaroubaceae, Simaba multiflora A.Juss. whose structure was established by X-ray diffraction analysis. 6α-Senecioyloxychaparrin $\text{2}$, the known 6α-senecioloyxychaparrinone $\text{3}$ and 9-methoxycanthin-6-one $\text{5}$ were also isolated ; their structure were determined by spectral means.     

Integer linear programming as a tool for constructing trees from quartet data

The task of the quartet puzzling problem is to find a best-fitting binary X-tree for a finite n-set from confidence values for the 3n4 binary trees with exactly four leaves from X, its fitness being measured by the sum of the confidence values of all "induced" four-leaves subtrees. We describe a method for finding an exact solution of this problem by integer linear programming. Similar procedures can also be used for finding, e.g. best-fitting "circular" networks. A crucial problem in this context is, of course, how to obtain the input confidence values for the quartet trees. We propose to use inner products of rate-matrix diagonals calculated for pairs of taxa and present the trees resulting from applying our approach to two data sets of up to 36 mitochondrial sequences of mammals including an outgroup.     

Synthesis and thermal properties of side-chain liquid crystalline polyethers with racemic and chiral backbone

Racemic and chiral [(4-cyano-4′-biphenyl)oxy] and [(4-methoxy-4′-biphenyl)oxy]methyloxiranes were prepared from racemic epichlorohydrin or racemic and chiral glycidols and polymerized in dimethylsulfoxide (DMSO) with Bu^tOK as the initiator system. Initial phase identifications were made by differential scanning calorimetry (DSC) and optical microscopy techniques and confirmed by X-ray diffraction measurements. Upon heating, all the monomers show only a crystal–isotropic phase transition. The racemic and chiral [(4-cyano-4′-biphenyl)oxy]methyloxiranes exhibit a nematic and a cholesteric monotropic phase, respectively. Methoxybiphenyl substituted polyethers are crystalline and insoluble in virtually all common solvents. Cyanobiphenyl substituted polyethers are soluble under the same experimental conditions and show enantiotropic liquid crystalline properties. The racemic polymer exhibits a nematic phase, while the optically active polymer forms a cholesteric phase.     

Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. 1. Influence of polyelectrolyte molecular weight

The synergistic adsorption and complexation of polystyrene sulfonate, PSS (a highly charged anionic polyelectrolyte), and dodecyltrimethylammonium bromide, C12TAB (a cationic surfactant), at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied as a function of PSS molecular weight by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously the solution electromotive force has been measured to track the polymer-surfactant interactions in the bulk solution. It has been found that there is a critical molecular weight for surface gelation as well as for bulk precipitation and aggregation. Furthermore, we show that for the lowest molecular weights, PSS adsorbs with C12TAB in compact layers at the air-water interface. In particular, for mixtures of C12TAB with the monomer compound of the PSS repeat unit (e.g. Mw = 208), interfacial complexation is found to be similar to that of catanionic mixtures (mixtures of surfactants of opposite charge).     

Electrogenerated radical anions in room-temperature ionic liquids

The sequential two-electron reduction of benzaldehyde to the radical anion and dianion species in 1-butyl-3-methylimidazolium triflimide and 1-butyl-1-methylpyrrolidinium triflimide is reported. In 1-butyl-1-methylpyrrolidinium triflimide, the heterogeneous electrochemistry and follow-up chemical reactivity are essentially equivalent to that in conventional molecular-solvent-based electrolytes where no interaction with the media is observed. In 1-butyl-3-methylimmidazolium triflimide, reduction occurs via the same two heterogeneous processes; however, the apparent heterogeneous rate constants are smaller by ca. 1 order of magnitude which leads to quasi-reversible electrochemical behavior. Since the bulk viscosities of the liquids are similar, the slower heterogeneous kinetics are attributed to local interfacial viscosity due to local ordering in the imidazolium-based medium. Also, a dramatic anodic shift in the reduction potentials is observed in 1-butyl-3-methylimidazolium triflimide media that is attributed to a stabilizing interaction of the radical anion and dianion species with the imidazolium cation.     

Mirror‐Image Packing Provides a Molecular Basis for the Nanomolar Equipotency of Enantiomers of an Experimental Herbicide

Programs of drug discovery generally exploit one enantiomer of a chiral compound for lead development following the principle that enantiomer recognition is central to biological specificity. However, chiral promiscuity has been identified for a number of enzyme families, which have shown that mirror‐image packing can enable opposite enantiomers to be accommodated in an enzyme's active site. Reported here is a series of crystallographic studies of complexes between an enzyme and a potent experimental herbicide whose chiral center forms an essential part of the inhibitor pharmacophore. Initial studies with a racemate at 1.85 Å resolution failed to identify the chirality of the bound inhibitor, however, by extending the resolution to 1.1 Å and by analyzing high‐resolution complexes with the enantiopure compounds, we determined that both enantiomers make equivalent pseudosymmetric interactions in the active site, thus mimicking an achiral reaction intermediate.     

Influence of surfactant counterions during electrophoretic particle deposition

This study demonstrates the influence of a cationic surfactant on colloidal particle electrodeposition (migration and adhesion). Three cetyltrimethylammonium salts (CTA+) with various counterions (bromide, chloride, and hydrogenosulphate) were studied. Particle transport toward the electrode was driven by the electrophoretic force. Once particles reached the electrode, a wide variety of behaviors were observed, depending on surfactant concentration and counterions: particles would stick permanently or slide along the electrode surface, remain or detach upon potential switching, act as nuclei for aggregate growth, or produce a homogeneous particle film. The experimental results also demonstrate the specific influence of surfactant counterions on the deposited film morphology.