Mutual diffusion and thermodynamics in the blends of polystyrene and tetramethylbisphenol-A polycarbonate

A study was made of miscible polymer blends of deuterated polystyrene (d-PS) and tetramethylbisphenol-A polycarbonate (TMPC). The Flory interaction parameter χ was obtained from the relation between mutual and tracer diffusion coefficients, D? and D^*, which were measured by forward recoil spectrometry. The temperature dependence of diffusion at PS weight fractions ω of 0.25 and 0.5, and the composition dependence at temperatures 45°C above the glass transition temperature, T_g, were investigated. A stronger dependence of χ on both temperature (at ω = 0.5) and composition was observed in comparison with other miscible binary polymer blends involving PS. Analysis using the generalized lattice-fluid model of Sanchez and Balazs¹ showed that the incorporation of a significant specific interaction is needed to explain the temperature dependence of χ. The diffusion coefficients obtained in the one-phase region were extrapolated to the two-phase region, and these were compared with the effective diffusion coefficient extracted from phase separation dynamics measured by light scattering.² A significant discrepancy between the extrapolated and effective diffusion coefficients was observed. © 1995 John Wiley & Sons, Inc.     

Rapid high-yield purification of canine intestinal motilin and its complete sequence determination

Canine motilin has been purified from small amounts of canine intestine in a form suitable for microsequence analysis. The sequence determined is: Phe-Val-Pro-Ile-Phe-Thr-His-Ser-Glu-Leu-Gln-Lys-Ile-Arg-Glu-Lys-Glu-Arg- Asn-Lys - Ile-Arg-Asn-Lys-Gly-Gln. Canine motilin differs from porcine motilin at five positions. The rapid, high-yield (24% overall yield) microisolation techniques used for canine motilin should be suitable for the isolation of other basic peptides found in low levels in tissue that is available only in limited amounts. These methods should make the isolation and sequence determination of human brain and gut peptides more readily achievable.     

The electronic Raman spectrum of cobalt doped MgO

The energies of the ⁴T_1g states of Co²⁺ as a dilute substitutional impurity in MgO relative to the ground Λ_6g doublet have been found by low temperature Raman spectroscopy to be two Λ_8g states at 305 ± 3 cm^?1 and 930 ± 3 cm^?1; the remaining Λ_7g energy is predicted to be in the 980–1010 cm^?1 range the corresponding Λ_6g → Λ_7g Raman transition being weak and buried in the extensive two-phonon background. A second-order perturbation calculation which couples the spin-orbit states to both E_g and T_2g modes of vibration gives a weak but important Jahn-Teller stabilization energy for the Λ_8g states.     

Hybrid Modelling for Robust Solving

We study a balanced academic curriculum problem and an industrial steel mill slab design problem. These problems can be modelled in different ways, using both Integer Linear Programming (ILP) and Constraint Programming (CP) techniques. We consider the utility of each model. We also propose integrating the models to create hybrids that benefit from the complementary strengths of each model. Experimental results show that hybridization significantly increases the domain pruning and decreases the run-time on many instances. Furthermore, a CP/ILP hybrid model gives a more robust performance in the face of varying instance data.     

The effect of replacing a benzene ring with a saturated six-membered ring on the mesomorphic properties of 4,4'-disubstituted diphenyldiacetylenes

A limited selection of ring modified diphenyldiacetylenes of the type where A=, Y=C_nH_2n+1, CF₃, F, COMe, NH₂, and NMe₂, and A=, trans and cis with Y=F and trans with Y=C₃H₇, were synthesized. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These properties were generally poorer than those found in the parent benzene compounds. This was also true of some pyrimidine analogues reported earlier. Birefringence values also decreased as expected.