Experiment and modelling of birefringent flows using commercial CFD code

It is well-known that certain fluids are birefringent and when flows are viewed in polarised light interference fringes are observed. The fringes are caused by a phase shift in the light passing through the fluid and are proportional to the integral of the maximum shear strains in the fluid. In order to understand what is happening within the three dimensional flow and overcome the difficulties due to this integration, additional computational or experimental information is needed.

In this work, a commercially available computer code (Fluent) is used for the first time to model the flows. The flow data are then exported to a spreadsheet where the shear rates are integrated across the field and then banded for graphical output. The results from this are then compared to results generated from birefringent flow experiments and the agreement is found to be good since the modelled fringes show the same patterns as those in the experiment. This novel use of computational and experimental techniques together will allow quantitative analysis of three-dimensional flows in the future.

Currently, there are still a lot of empirical variables involved in fitting the computational fringes to the experiment, but the results of this preliminary study show that this is a promising approach to this type of problem.     

Copper and palladium complexes with N-heterocyclic carbene ligands functionalised with carboxylate groups

The new imidazolium salts functionalised with the trimethylsilyl ester group 1a–c, were easily obtained by quaternisation of alkyl- or aryl-imidazoles with trimethylsilyl bromoacetate. Salt 1a was isolated and fully characterised. It reacted with mesityl copper (Cu₅Mes₅) under trimethylsilyl abstraction to form the complex 2. Methanolysis of 1a–c gave good yields of the carboxylic acid functionalised imidazolium salts 3a–c. Deprotonation of the latter in liquid ammonia led to the zwitterionic imidazolium carboxylates 4a–c. Reaction of 4a with (Cu₅Mes₅) gave solutions from which the insoluble polymeric 5a crystallised slowly. Generation of the carboxylate-functionalised NHC in situ followed by reaction with Pd(OOCCH₃)₂ gave the new complex 6a in which the NHC-carboxylate ligand is chelate bidentate.     

Spectral Measures and Generating Series for Nimrep Graphs in Subfactor Theory II: <Emphasis Type="Italic">SU</Emphasis>(3)

We complete the computation of spectral measures for SU(3) nimrep graphs arising in subfactor theory, namely the SU(3) ADE{SU(3) \mathcal{ADE}} graphs associated with SU(3) modular invariants and the McKay graphs of finite subgroups of SU(3). For the SU(2) graphs the spectral measures distill onto very special subsets of the semicircle/circle, whilst for the SU(3) graphs the spectral measures distill onto very special subsets of the discoid/torus. The theory of nimreps allows us to compute these measures precisely. We have previously determined spectral measures for some nimrep graphs arising in subfactor theory, particularly those associated with all SU(2) modular invariants, all subgroups of SU(2), the torus \mathbbT², SU(3){\mathbb{T}^2,\,SU(3)}, and some SU(3) graphs.     

Yttrium Complexes of Arsine,Arsenide, and Arsinidene Ligands

Deprotonation of the yttrium–arsine complex [Cp′₃Y{As(H)₂Mes}] ( 1 ) (Cp′=η⁵‐C₅H₄Me, Mes=mesityl) by nBuLi produces the μ‐arsenide complex [{Cp′₂Y[μ‐As(H)Mes]}₃] ( 2 ). Deprotonation of the As H bonds in 2 by nBuLi produces [Li(thf)₄]₂[{Cp′₂Y(μ₃‐AsMes)}₃Li], [Li(thf)₄]₂[ 3 ], in which the dianion 3 contains the first example of an arsinidene ligand in rare‐earth metal chemistry. The molecular structures of the arsine, arsenide, and arsinidene complexes are described, and the yttrium–arsenic bonding is analyzed by density functional theory.     

Bestimmung einzelner Elemente in organisehen Verbindungen

Ohne Zusammenfassung     

The Influence of pH and Temperature on the Equilibrium and Dynamic Surface Tension of Aqueous Solutions of Sodium Oleate

For aqueous solutions of sodium oleate, the dynamic surface tension (using the maximum bubble pressure technique) and the equilibrium surface tensions (using the du Noüy ring method) were studied. Experiments were carried out within the pH range 7 to 13 and at temperatures from 20 to 60 degrees C. From the equilibrium surface tension studies at 25 degrees C, a wide variation in surface activity was found to occur in the premicellar concentration range, depending on pH and oleate concentration, and this was explained on the basis of the formation of strongly surface-active premicellar species. It was also shown that the critical micelle concentration (cmc) of the system increased with pH within the pH range 7-12. Dynamic surface tension experiments were carried out from 20 to 60 degrees C at concentrations beyond the cmc in alkaline solutions, and the adsorption kinetics at the air/solution interface were analyzed using established theoretical diffusion models. From these data, the effective diffusion coefficients (D(eff)) for the oleate species were determined and the presence of an interfacial activation barrier in the diffusion process was confirmed. It was found that the D(eff) values obtained within the temperature range from 40 to 60 degrees C at 2-3 mM were in general agreement with previously reported values for the oleate dimer obtained by pulse-gradient FT-NMR. Furthermore, D(eff) significantly increased with temperature and also increased with concentration at higher temperatures (>40 degrees C). Copyright 2001 Academic Press.     

The influence of interparticle surface forces on the coagulation of weakly magnetic mineral ultrafines in a magnetic field

In this paper, it is shown that the coagulation of dispersions of weakly magnetic mineral ultrafines (such as hematite and chromite) in an external magnetic field can be described theoretically by invoking interparticle forces. Essentially, coagulation occurs when the short-range London—van der Waals interactions and the long-range magnetic forces outweigh the stabilizing electric double layer repulsion. From classical colloid chemistry theory, we have calculated the various components of the potential energy for different-sized particles at a series of ionic strengths and magnetic field intensifies. Principles governing the stability of the suspensions were derived and the computations lead to the establishment of criteria which can be used to predict the stability of the suspensions of weakly magnetic oxide mineral ultrafines in a “wet magnetic separation process”.

Experimentally, the magnetic-field induced coagulation of ultrafines of natural hematite and chromite in aqueous suspensions at moderate ionic strength was investigated using a laboratory-scale electromagnetic solenoid. The experimental results relate the coagulation process (as determined by magnetosedimentation analysis) to particle size, slurry pH and the external magnetic field. In the magnetic fields, maximum coagulation occurred near the pH of the point of zero charge (pH_PZC) of the minerals (where the electrostatic double layer repulsion was reduced to a minimum) enabling the particles to enter the “primary minimum” energy sink. In contrast, in cases where the electrostatic repulsion was not suppressed, the long-range magnetic forces enabled coagulation to occur in the “secondary minimum”. This caused the formation of chains which appeared to be relatively stable at enhanced rates of settling. The experimental results could be interpreted from a theoretical analysis of the interparticle forces controlling the process.     

Strain-field investigations with plane diffraction gratings

The development of means for producing small, separate, plane diffraction gratings as integral parts of the surfaces of flat metal specimens has led to modification of the method of Bell and to the investigation of strain fields by study of diffraction phenomena. Choice of a particular diffraction-strain relationship and the use of master gratings in conjunction with diffraction gratings to be used as strain gages permits use of simple optical instrumentation. The diffraction phenomena from multiple gages at the same orientation may be photographed simultaneously during loading for subsequent analysis, and instrumentation in the form employed permits resolving strain increments of magnitude 0.0008 in the range 0.0030 to 0.030.     

A computer-based spectrophotometric study of the kinetics of the aquation of halogenopentammine-chromium(III) perchlorate

Conventional determinations of rate constants k from absorption spectra employ a few selected wavelengths: by digitizing the complete spectrum computer calculations of k can be made at most wavelengths, and hence with better precision. This has here been satisfactorily tested for the aquation of halogenopentamminechromium(III) perchlorate. Two independent procedures are described, which are approximately equally onerous on computer time. Additionally, these procedures are shown to yield identical computer-generated spectra for the halogeno-complex before aquation commences, and accurate time infinity spectra, of the aquo-complex, for long half-life reactions. They also efficiently eliminate the effects of spectrophotometer instability over long periods of time.     

Gas phase thermal diffusivities by a thermal lens technique

A simplified design of thermal lens apparatus is presented in which a chopped cw argon laser beam produces a transient thermal lens in a cylindrical gas cell. The axial intensity variation of a cw helium-neon laser probing this lens is analysed to yield the thermal diffusivities and thus the thermal conductivity coefficients of Kr, CO₂, CH₄, C₂H₆, C₃H₈, C₃H₆ and C₄H₁₀ as 9.4 × 10^?3 ± 4%, 1.6 × 10^?2 ± 3%, 2.98 × 10^?2 ± 4%, 2.03 × 10^?2 ± 4%, 2.05 × 10^?2 ± 7%, 1.6 × 10^?2 ± 8% and 1.9 × 10^?2 ± 8% respectively in W m^?1 K^?1 at 300 K. The method is rapid, requiring only that the sample be transparent at both laser frequencies used. A simplified mathematical analysis is shown to be adequate for this system. For the conditions specified, self-lensing of the argon laser beam is shown to be compensated by using an effective laser beam diameter.