Green's functions associated with the edth operators

An integral representation for the inverses of the differential operators called edth is given in the two cases of particular interest. This operator plays a large role in the study ofH spaces and of self-dual solutions to the Yang-Mills field equations in the asymptotic domain.     

Melting behavior of poly(ether ether ketone) in its blends with poly(ether imide)

We detail the melting behavior of poly(ether ether ketone) (PEEK) and investigate its melting behavior in miscible blends with poly(ether imide) (PEI). The determination of the equilibrium melting point (T_m⁰) of PEEK is discussed by considering its inhomogeneous morphology. T_m⁰ is obtained by a long extrapolation of a Hoffman–Weeks plot to 384°C. Hindrance of PEEK crystal reorganization induced by PEI during heating is observed over the blend composition investigated (20–75 wt % PEEK). This behavior is correlated with the incorporation of PEI in the interlamellar zones of PEEK crystals. The interaction parameter χ of PEEK/PEI blends is estimated by the equilibrium melting point depression. This gives the interaction density B = ?1.2 cal/cm³, and x = ?0.40 at 400°C. © 1993 John Wiley & Sons, Inc.     

A convenient route for the synthesis of s,s-and R,R-warfarin alcohols

S,S-and R,R-warfarin alcohols 3 are prepared in good yield and in 99% d.e. (diastereomeric excess) by the reaction of S- or R-warfarin 1 with S or R-Alpine-Hidride 2.     

Blends of poly(butylene terephthalate) and a polyarylate before and after transesterification

Blends of poly(butylene terephthalate) (PBT) and a copolyester of bisphenol-A with 50% terephthalate-50% isophthalate (PAr), before and after transesterification, have been studied by thermal and dynamic mechanical tests to determine crystallinity and phase behavior. Blends without transesterification, as prepared by solution precipitation, show a single T_g, indicating amorphous miscibility of PBT and PAr. A melting-point depression for PBT crystals is not observed; this means that PBT crystallizes excluding PAr and the entropy of melting is small. The highest fractional crystallinity for PBT is obtained at 20-35% of PAr. Transesterified blends were obtained by holding the physical blends at 250°C for up to 16 h. The transesterified systems show higher T_g's than the corresponding physical blends and also show a marked melting-point depression and lesser PBT crystallinity at the corresponding increased PAr content.     

Trapping efficiencies of various collection solvents after supercritical fluid extraction

A polarity test mix consisting of acetophenone, N, N-dimethylaniline, naphthalene, decanoic acid, 2-naphthol, and n-tetracosane was spiked onto sand, and extracted with supercritical carbon dioxide, to evaluate the collection efficiency of various solvents and solvent mixtures. Nine single collection solvent systems and four mixed collection solvent systems were studied. When one-component collection solvents were employed, quantitative (above 90%) recovery of all analytes was not possible. With mixed collection solvents, recoveries of 90% or better with all analytes studied were possible.     

Reproducibility in capillary supercritical fluid chromatography: Comparison of injection techniques

An analysis of the precision obtained using commercially available microvalve injectors is reported for three modes of injection: conventional split; timed-split; and direct. Results from this study show that good precision (< 3% RSD for external standard and < 1% RSD for internal standard methods) can be obtained with capillary supercritical fluid chromatography (SFC). However, particular attention must be paid to the type of valve used, the orientation of the column relative to the valve, the mode of interfacing or connecting the column to the valve, and the type of pressure or density programming used for the analysis as all of these factors will affect the reproducibility.     

Solid-state extrusion of chain-extended polyethylene

Billets of chain-extended polyethylene were prepared from Alathon 7050 (M_w 59,000, M_n 19,000) in an Instron capillary rheometer by crystallization at a constant pressure of 460 MPa, at a series of teimperatures from 198 to 221°C corresponding to varying degrees of undercooling. This gives chain-extended morphologies with a range of crystallinites and lamellar thicknesses. The billets were then solid-state extruded at 100°C through a conical die with 20° entrance angle up to an extrusion draw ration 23.4. Thermal behavior was studied with differential scanning calorimetry. The orientation function measured by wide-angle x-ray diffraction showed higher orientation function measured by wide-angle x-ray diffraction showed higher orientation at equivalent draw ratio when the initial billets were crystallized at lower temperatures. Drawing efficiency, defined as the ratio of molecular draw ratio (from shrinkage) to extrusion draw ratio correspondingly increases, reaching a maximum of 0.71 in our solid-state extrusion. These studies show that highly chain-extended polyethylene, i.e., with few chain entanglements, draws poorly. Drawability was improved by increasing chain entanglements by lowering the crystallization temperature. Electron micrographs of fracture surface replicas of extrudates revealed the coexistence of undeformed, tilted, partially drawn lamellae and fibrillar structure consistent with the cahange of morphologies in Peterlin's model of plastic deformation.