A systematic study of the microwave and thermal cure kinetics of the TGDDM/DDS and TGDDM/DDM epoxy-amine resin systems

The microwave and thermal cure processes for the epoxy-amine systems N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl methane (TGDDM) with diaminodiphenyl sulfone (DDS) and diaminodiphenyl methane (DDM) have been investigated. The DDS system was studied at a single cure temperature of 433 K and a single stoichiometry of 27 wt% and the DDM system was studied at two stoichiometries, 19 and 32 wt%, and a range temperatures between 373 and 413 K. The best values the kinetic rate parameters for the consumption of amines have been determined by a least squares curve Ft to a model for epoxy-amine cure. The activation energies for the rate parameters for the MY721/DDM system were determined as was the overall activation energy for the cure reaction which was found to be 62 kJ mol(-1). No evidence was found for any specific effect of the microwave radiation on the rate parameters, and the systems were both found to be characterized by a negative substitution effect. Copyright (C) 2001 John Wiley & Sons, Ltd.

Cohesion among nurses: a comparison of bedside vs. charge nurses' perceptions in Australian hospitals

Aim. This study examines the extent to which hospital nurses view their working environment in a positive sense, working as a cohesive group. Background. Despite the fact that nursing in Australia is now considered a profession, it has been claimed that nurses are an oppressed group who use horizontal violence, bullying and aggression in their interactions with one and other. Methods. After ethical approval, a random sample of 666 nurses working directly with patients and all 333 critical care nurses employed in three large tertiary Australian hospitals were invited to participate in the study in the late 1990s. A mailed survey examined the perceptions of interaction nurses had with each other. The hypothesis, that level of employment (either Level I bedside nurses or Level II/III clinical leaders) and area of work (either critical care or noncritical care) would influence perceptions of cohesion, as measured by the cohesion amongst nurses scale (CANS) was tested. Results. In total 555 (56%) surveys were returned. Of these, 413 were returned by Level I and 142 by Level II/III nurses. Of this sample, 189 were critical care and 355 noncritical care nurses. There was no difference between Level I and II/III nurses in mean CANS scores. It is interesting to note that the item rated most positively was, 'nurses on the units worked well together', however, the item rated least positive was 'staff can be really bitchy towards each other' for both Level I and II/III nurses. There was no difference in CANS scores between critical care and noncritical care nurses. Conclusions. Nurses working in Australian hospitals perceived themselves to be moderately cohesive but, as would be expected in other work settings, some negative perceptions existed.

Isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate characterized as cobalt(III) complexes

The major trans (1) and minor cis (2) isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate have been characterized as the complexes [Co(1)](ClO4) and [Co(H-2)(OH2)]Cl(ClO4).H2O. The former crystallized in the C-2/c space group and the latter in the P2(1)/c space group, with cell parameters a 16.258(7), b 9.050(3), c 15.413(6) Angstrom, beta133.29(3)degrees, and a 9.694(4), b 16.135(1), c 12.973(5) Angstrom, beta 93.00(2)degrees, respectively. Their characterization completes identification of the respective trans and cis isomers for the series of C-pendant macrocycles also including 1,4,8,11-tetraazacyclotetradecane-6-amine-13-carboxylate ((3), (4)) and 1,4,8,11-tetraazacyclotetradecane-6,13-diamine ((5), (6)). The complexes show limited distortion from octahedral geometry with the strain in the presence of the coordinated C-pendant carboxylate significantly reduced compared with that for the C-pendant amine in analogues, a consequence mainly of six-membered as opposed to five-membered chelate rings involving the pendant donor. A comparison of the physical properties for the trans isomers of the octahedral complexes of (1), (3), and (5), which reflect progressively increasing strain, is presented.