Spinodal decomposition in solid isotopic helium mixtures

We report the first observations of spinodal decomposition in solid helium isotopic mixtures, using NMR measurements. The experiments were performed at a 3He concentration of 50% where the transition proceeds through the critical point. We used an initial pressure such that the system remained solid. Our observations indicate that the transition occurs by the mechanism of spinodal decomposition and we are able to study its evolution in real time.     

The photoelastic properties of polydimethylsiloxane rubbers

The temperature dependence of the optical anisotropy and of the mean square end-to-end distance of polydimethylsiloxane chains have been derived from photoelastic measurements. The rotational isomeric chain model, including the interaction of neighboring bond rotations, is insufficient to interpret the data completely.

The non-Gaussian behavior of short-chain networks of polydimethylsiloxane is compared with the theoretical models of Treloar and Gotlib. Neither is found to be completely satisfactory. Crude estimates of the number of monomers per equivalent randomly jointed link are obtained, and the usefulness of the freely jointed chain model is discussed.     

Hilbert forms for a Finsler metrizable projective class of sprays

The projective Finsler metrizability problem deals with the question whether a projective-equivalence class of sprays is the geodesic class of a (locally- or globally-defined) Finsler function. In this paper we use Hilbert-type forms to state a number of different ways of specifying necessary and sufficient conditions for this to be the case, and we show that they are equivalent. We also address several related issues of interest including path spaces, Jacobi fields, totally-geodesic submanifolds of a spray space, and the equivalence of path geometries and projective-equivalence classes of sprays.     

Quantitative electron diffraction: From atoms to bonds

The development of new transmission electron microscopes with energy-filtering capability together with the increase in computer power over the past few years has enabled electron diffraction from inorganic crystals to become a quantitative and accurate science. With the introduction of new techniques and data analysis and with the advantage of a nanometre-sized probe, electron diffraction now rivals X-ray and neutron methods in many aspects of crystallography and solid-state physics. In this article, we have discussed two new developments which highlight the progress made in this area. First, a new method for ab-initio structure determination is explained and an example given to show its success. Second, energy-filtered diffraction patterns are used to refine the scattering potential of a crystal so that the bonding charge density can be reconstructed.     

Pyridinium p-toluenesulfonylmethylide as a formyl anion equivalent

Pyridinium $\text{p}$-toluenesulfonylmethylide serves as a formyl anion equivalent and, in the presence of an alcohol, undergoes 1,4-addition to $\text{N}$-substituted maleimides to give alkoxy- (or aryloxy)-methylene-succinimides. The protected aldehyde group can be liberated readily.     

Poly(D,L-lactide-co-glycolide) dispersions containing pluronics: from particle preparation to temperature-triggered aggregation

In this work the preparation mechanism, properties and temperature-triggered aggregation of poly(D, L-lactide- co-glycolide) (PLGA) dispersions are investigated. The dispersions were prepared by interfacial deposition in aqueous solution containing Pluronic L62 (EO(6)PO(30)EO(6)) or F127NF (EO(101)PO(56)EO(101)), where EO and PO are ethylene oxide and propylene oxide, respectively. PLGA dispersions were also prepared in the absence of added Pluronic for comparison. The PLGA particles were characterized using SEM, photon correlation spectroscopy and electrophoretic mobility measurements. It was found that the hydrodynamic diameter (d) increased with PLGA concentration used in the organic solvent phase ( C PLGA(o) ). The value for d was proportional to C(PLGA)(o) (1/3). The value for d increased upon addition of 0.04 M NaNO(3) which demonstrated the importance of electrostatic interactions during particle formation. Electrophoretic mobility measurements were conducted as a function of pH and the data used to estimate the Pluronic layer thicknesses on the PLGA particles. The layer thickness was greatest for the PLGA particles prepared in the presence of Pluronic F127NF. PLGA dispersions containing Pluronic L62 exhibited temperature-triggered aggregation in the presence of 0.15 M NaNO(3). It was found that the critical temperature for dispersion aggregation (T(crit)) was comparable to the cloud point temperature ( T(cp)) for the parent Pluronic L62 solution. Conditions were established for achieving temperature-triggered aggregation at body temperature for PLGA particle/Pluronic L62 dispersions under physiological ionic strength and pH conditions. The PLGA/Pluronic L62 mixtures studied may have potential for use as injectable biodegradable implants for controlled release applications.     

The interaction of EDTA with barium sulfate

Ethylenediaminetetraacetic acid (EDTA) is a known complexing agent that interacts with a host of cations. In this paper, various techniques are used to elucidate the mechanism of interaction between EDTA and barium sulfate surfaces. It is shown that complexation with metal ions is not sufficient to explain the inhibition of barite crystallization but that other processes such as chemisorption must also occur. EDTA is shown to always adsorb as the mono-protonated species - suggesting that the molecule is able to lose a proton when it adsorbs at lower pH. Molecular modelling shows that the interaction of the surface barium ions with the carboxylate group is an important one. Finally, in situ turbidity measurements provide information about the mechanism of nucleation/growth modification. It is found that the EDTA molecule inhibits barium sulfate nucleation and that this could be its primary means of inhibiting precipitation of barium sulfate.     

Ultrasonic wave velocities and attenuation in IVb-Vb-VIb chalcogenide glasses: 2–300 K

The velocities and attenuation of longitudinal and shear ultrasonic (12 MHz) waves have been measured for several chalcogenide glasses (Ge₁₀Si₁₂As₃₀Te₄₈, Ge₂₀As₃₀Se₅₀, Si₂₀As₃₂Te₄₈, Ge₁₀Si₁₂As₂₉Te₄₉, Ge₁₂S₁₄As₃₅Te₄₉). The bulk, shear and Young's moduli and the Poisson ratio are found to be insensitive to the glass composition. The temperature dependences of the longitudinal and shear-wave velocities are negative at higher temperatures and approach 0 K with a zero slope. The ultrasonic attenuation does not exhibit either the broad loss peak or the smaller low-temperature peak found in many other glasses: the elastic and anelastic behaviour is quite different from that of oxide glasses — no evidence for the existence of two-level systems has been obtained from the ultrasonic measurements.