The multi‐stage centred‐scheme approach applied to a drift‐flux two‐phase flow model

For two‐phase flow models, upwind schemes are most often difficult do derive, and expensive to use. Centred schemes, on the other hand, are simple, but more dissipative. The recently proposed multi‐stage (MUSTA ) method is aimed at coming close to the accuracy of upwind schemes while retaining the simplicity of centred schemes. So far, the MUSTA approach has been shown to work well for the Euler equations of inviscid, compressible single‐phase flow. In this work, we explore the MUSTA scheme for a more complex system of equations: the drift‐flux model, which describes one‐dimensional two‐phase flow where the motions of the phases are strongly coupled. As the number of stages is increased, the results of the MUSTA scheme approach those of the Roe method. The good results of the MUSTA scheme are dependent on the use of a large‐enough local grid. Hence, the main benefit of the MUSTA scheme is its simplicity, rather than CPU ‐time savings. Copyright © 2006 John Wiley & Sons, Ltd.     

Nuclear magnetic resonance spectroscopy of petroporphyrins : Self-aggregation effects, nuclear overhauser enhancements, and spin-lattice relaxation used in structural elucidation

The substitution pattern of the two major petroporphyrins of Marl Slate, the ETIO III and the C₃₂ DPEP, is determined by NMR spectroscopy alone, using self-aggregation effects, nuclear Overhauser enhancements and spin-lattice relaxation times. Protoporphyrin IX dimethyl ester was used as a model compound.     

Elucidation of the thermochemical properties of triphenyl- or tributyl-substituted Si-, Ge-, and Sn-centered radicals by means of electrochemical approaches and computations

Redox potentials of a number of triphenyl- or tributyl-substituted Si-, Ge-, or Sn-centered radicals, R(3)M(*), have been measured in acetonitrile, tetrahydrofuran, or dimethyl sulfoxide by photomodulated voltammetry or through a study of the oxidation process of the corresponding anions in linear sweep voltammetry. For the results pertaining to the Ph(3)M(*) series (including literature data for M = C), the order of reduction potentials follows Sn > Ge > C > Si, while for the two oxidation potentials, it is C > Si. The effect of the R group on the redox properties of R(3)Sn(*) is pronounced in that the reduction potential is more negative by 490 mV in tetrahydrofuran (390 mV in dimethyl sulfoxide) when R is a butyl rather than a phenyl group. The experimental trends have been substantiated through quantum chemical calculations, and they can be explained qualitatively by considering a combination of effects, such as charge capacity being most pronounced for the heavier elements, resonance stabilization present for the planar Ph(3)C(*) and all R(3)M(+)(), and finally a contribution from solvation. The solvation of R(3)M(-) is observed to be relatively strong because of a rather localized negative charge in the pyramidal geometry. However, there is no evidence in the calculations to support the existence of covalent interactions between solvent and anions. The solvation of R(3)M(+)() is relatively weak, which may be attributed to the planar geometry around the center atom, leading to more spread out charge than that for a pyramidal geometry. Although the calculated solvation energies based on the polarizable continuum model approach exhibit the expected trends, they are not able to reproduce the experimentally derived values on a detailed level for these types of ions. An evaluation of the general performance of the continuum model is provided on the basis of present and previous studies.     

Method for enantiomeric purity of a quinuclidine candidate drug by capillary electrophoresis

A chiral procedure based on EKC was developed and validated for determination of the enantiomeric purity of PHA-543613, a drug candidate that was under development for treatment of the cognitive deficits of Alzheimer's disease and schizophrenia. Separation of enantiomers is accomplished via differential, enantiospecific complexation with a single-isomer, precisely sulfated beta-CD and heptakis-6-sulfato-beta-CD (HpS-beta-CD). Both neutral and sulfated CDs were screened before selecting HpS-beta-CD as the chiral selector. The separation is conducted in a 61 cm x 50 microm uncoated fused silica capillary with 25 mM HpS-beta-CD in pH 2.50, 25 mM lithium phosphate as the separation buffer with detection at 220 nm. Application of reverse polarity at -30 kV results in an elution time of about 12 min for PHA-543613 and 13 min for the undesired S-enantiomer. Quantification is versus an authentic reference S-enantiomer as an external standard in combination with an internal standard. The procedure was validated over the range 0.1-2.0% w/w. The detection limit is 0.01-0.02%. The amount of distomer intrinsic to the drug substance is about 0.1% or less. The developed method was used to generate stability data on multiple lots: in one case for up to 3 years.     

Numerical approach for generic three-phase flow based on cut-cell and ghost fluid methods

In this paper, we introduce numerical methods that can simulate complex multiphase flows. The finite volume method, applying Cartesian cut-cell is used in the computational domain, containing fluid and solid, to conserve mass and momentum. With this method, flows in and around any geometry can be simulated without complex and time consuming meshing. For the fluid region, which involves liquid and gas, the ghost fluid method is employed to handle the stiffness of the interface discontinuity problem. The interaction between each phase is treated simply by wall function models or jump conditions of pressure, velocity and shear stress at the interface. The sharp interface method “coupled level set (LS) and volume of fluid (VOF)” is used to represent the interface between the two fluid phases. This approach will combine some advantages of both interface tracking/capturing methods, such as the excellent mass conservation from the VOF method and good accuracy of interface normal computation from the LS function. The first coupled LS and VOF will be generated to reconstruct the interface between solid and the other materials. The second will represent the interface between liquid and gas.     

Theoretical study of the singlet electronically excited states of N4

Vertical excitation energies for the lowest eleven singlet states of T_d N₄ were calculated using the TD-DFT method with the B3LYP functional, and at the EOM-CCSD level of theory. The vertical excitation energies for the five lowest-lying excited states were also obtained using the state-averaged CASSCF, CASPT2, CASPT3, and MRCI + Q methods. Our results show that the five lowest-lying states are of valence character. EOM-CCSD/d-aug-cc-pVTZ calculations predict that there are two weakly allowed optical transitions of T₂ symmetry at 10.44 and 10.82 eV. The transition to the third T₂ state, which is predicted to be at 10.89 eV, has an oscillator strength about one order of magnitude higher.     

Electrosorptive detection based on double-layer capacitance for selective anion monitoring in ion chromatography : Part 1. Mercury Electrodes

A novel scheme is presented for the detection of selected anions in ion chromatography, based on changes in differential double-layer capacitance, ΔC_d, for a metal electrode at a suitable electrode potential induced by specific anion adsorption. The detector in this liquid chromatography/double-layer capacitance (LC/DLC) arrangement is a hanging or dropping mercury electrode in a large-volume wall-jet configuration. The anions observed to be detected readily by this approach include chloride, bromide, iodide, azide, thiocyanate, and thiosulfate. The relationship between ΔC_d and the analyte concentration can be arranged to be approximately linear at least over the range 1–100 mg l^?1. An attractive feature of the technique is its insensitivity to ionic concentration gradients in the flowing stream. Another virtue of LC/DLC is its selectivity, although it is less sensitive for the detection of complexing anions than amperometric detection based on mercury oxidation. Dual detection schemes are also devised, involving monitoring double-layer capacitance at two potentials or combined with amperometric detection.     

REDUCTION BY NEAR-ULTRAVIOLET (334 nm) LIGHT OF E. COLI CAPACITY FOR PHAGE GROWTH DEPENDS UPON THE rel GENE AND 4-THIOURIDINE

Abstract— Near-ultraviolet radiation (near UV; 300–380 nm) has long been known to produce a transient reduction of the capacity of bacteria to support phage growth. The present work shows that, at high fluenœs (40–100 kJ/m²), 85% of 334-nm-induced reduction of capacity in Escherichia coli B/r requires the rel gene; that is, it results from rel -gene activity caused by the near-UV treatment. This rel -gene activity leads to (1) a bacterial growth delay and concomitantly lowered bacterial metabolism, and (2) a parallel delay in phage development, with a considerable depression of burst size. We propose that the observed effects on phage development are a consequence primarily of the lowered bacterial metabolism, but they may also result partly from a direct inhibition of phage DNA synthesis by the rel gene product, these effects together leading to the observed reduction of capacity in a rel ⁺ strain. The remaining 15% of capacity reduction, observed in a rel strain, has an unknown mechanism, but does appear to involve a delay in phage development.
At least 95% of the total capacity reduction observed in the rel ⁺ strain in the range 40–100 kJ/m² requires the presence of 4-thiouridine, an unusual base in E. coli transfer RNA, which is presumably both the chromophore and the target for near-UV-induced capacity reduction.     

Simplicial gauge theory and quantum gauge theory simulation

We propose a general formulation of simplicial lattice gauge theory inspired by the finite element method. Numerical tests of convergence towards continuum results are performed for several SU(2) gauge fields. Additionally, we perform simplicial Monte Carlo quantum gauge field simulations involving measurements of the action as well as differently sized Wilson loops as functions of β.