Morphology and thermo-mechanical properties of new hybrid coatings based on polyester/melamine resin and pyrogenic silica

Polyester/melamine (PM)-based formulations used in coil-coating applications were modified with pyrogenic silicas of different types. The influence of the chemical modification of the silica surface on various properties was investigated. The viscosity of filled PM formulations was measured. Transmission electron microscopy and dynamic mechanical measurements were used to characterize nanocomposite films. Roughness and gloss measurements were done on nanocomposite coatings. The results show that the viscosity and morphology observed are directly linked to the balance and nature of the interactions developed between the silica surface and the organic medium. Both hydrophilic and hydrophobic silica lead to too high viscosity of the filled formulation, to different silica dispersion and, as a consequence, to low gloss coatings. However with an adequate organo-modification of the silica, formulations compatible with the process and having a high gloss can be obtained. Additionally, the surface modification of silica has no obvious influence on the dynamic mechanical properties.     

Kinetics modeling of a modified epoxy–amine formulation cured by thermal and microwave energy

The reaction kinetics of a rubber-modified epoxy formulation cured by microwave or thermal energy were investigated. Two phenomenological models were developed to predict the time and temperature dependence of the conversion for the neat and the modified systems. Good agreement was observed between the kinetic models and experimental results generated by chromatographic and calorimetric techniques. The same kinetic behavior was observed whatever the curing process (conventional or microwave heating). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 543–552, 1998     

An early and a late developing system for learning and retention in infant monkeys.

Separate groups of rhesus monkeys of different ages were tested in delayed nonmatching-to-sample and 24-hr concurrent discrimination-learning tasks considered to be measures of recognition memory and habit-formation systems, respectively, in an ontogenetic comparison of the development of these 2 systems. In Exp I, the visual-recognition abilities of 17 3-, 6-, or 12-mo-old Ss were measured, while 7 3-mo-old Ss were compared to adult controls on a discrimination-learning task in Exp II. Results show that infant Ss failed to learn the nonmatching task until they were approximately 4 mo old. With further maturation, learning ability gradually improved, but did not reach adult levels of proficiency even when Ss were 1 yr old. Postlearning evaluation with long delays and lists confirmed this slow ontogenetic development of recognition memory to adult levels of function. By contrast, 3–4 mo old Ss learned to discriminate long lists of object-pairs nearly as quickly as adults, despite 24-hr intertrial intervals. This striking dissociation in the ability of infants on the 2 tasks closely resembles the dissociation previously found in adults rendered amnesic by limbic lesions. Findings suggest that, whereas the nonlimbic habit system matures early in infancy, the limbic-dependent memory system develops more slowly. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The impact of selective amygdala, orbital frontal cortex, or hippocampal formation lesions on established social relationships in rhesus monkeys (Macaca mulatta).

Social dominance, personality ratings, and frequency, duration, and timing of social behaviors were measured pre- and postsurgically in 6 groups of rhesus monkeys (Macaca mulatta), each consisting of 1 sham-operated control and 1 monkey each with a selective amygdala, hippocampal, or orbital frontal cortex lesion. Unlike previous reports, none of the operated groups showed changes in social dominance postsurgery, although changes in other measures varied by lesion site. Although sham-operated monkeys displayed heightened avoidant, anxious, and aggressive behaviors, those with hippocampal lesions also showed increased exploration and excitability, along with reduced responses to affiliative signals. Amygdala lesions yielded several personality changes that precluded positive social interactions (increased exploration and excitability, decreased affiliation and popularity) and altered responses to threatening social signals. By contrast, monkeys with orbital frontal lesions were involved in more aggressive interactions and responded differently to both affiliative and threatening signals. Although several findings differ from earlier nonhuman primate studies, they are largely in agreement with human data and emphasize the context-specific nature of social behavior studies. Interpretation of results in relation to cognitive processes mediated by each structure is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative Determination of Acetaminophen in Pharmaceutical Formulations Using Differential Scanning Calorimetry. Comparison with Spectrophotometric Method

In this paper our previous researches dealing with compatibility, thermoanalytical characterization, the kinetics of thermal degradation of acetaminophen, either pure or contained in some commercial pharmaceutical formulations, have found applications outlets. In a previous investigation the possible interactions between acetaminophen and four excipients contained in the commercial pharmaceutical formulations were tested. As a continuation of this research in the present study an analytical method based on differential scanning calorimetry (DSC) was applied to determine the acetaminophen content of four commercial pharmaceutical formulations. For a fifth drug it was shown that the method is not applicable owing to observed incompatibility with one of the excipients. Finally, the analytical results obtained were compared with those derived from two UV spectrophotometric methods (one, i.e., “direct method,” recommended by the Pharmacopeia and the other based on the first-order derivative UV spectra).     

Human platelets release a paf-acether: Acetylhydrolase similar to that in plasma

Intact washed human platelets aggregated in response to paf-acether (paf) and did not metabolize [³H]paf at concentrations up to 10 nM. However, when platelets were lysed by exposure to pH 9.5, resulting in 37.5±2.5% (mean ±SD, n=3) lactic dehydrogenase (LDH) release, 20.5±5.7% of the radioactivity was detected as labeled lyso paf and 5.7±3.1% as labeled alkylacylglycerophosphocholine. When platelets were aggregated with 0.5 IU/mL thrombin or high concentrations of paf (100 nM), they released a part of their acetylhydrolase without releasing LDH. In supernatants obtained from aggregated platelets, 21±2% or 10±2% (n=3), respectively, of the total platelet acetylhydrolase activity was detectedvs. none in supernatants of resting cells. The release of acetylhydrolase was concentration-and time-dependent and paralleled the release of PF 4, a marker for α-granules. The acetylhydrolase affinity for paf (K_m) measured in sonicates of resting and thrombin-activated platelets was 8.3±1.5 μMvs. 10.6±1.5 μM, n=5, n.s. in a “Mann Whitney” test. The latter K_m was slightly but significantly different (P<0.05, n=5) from that of the thrombin-released acetylhydrolase (7.9 ±1.5 μM) and that of the latter was itself different from plasma acetylhydrolase (5.3±0.5,P<0.05, n=5). Addition of plasma (acid-treated to inactivate acetylhydrolase) decreased the K_m value of supernatant acetylhydrolase to 6.1±1.4 μM. All preparations of acetylhydrolase exhibited similar pH requirements and sensitvity to various inhibitors. Thus paf and thrombin cause release of acetylhydrolase from platelets in parallel with release of the α-granule marker PF4. This phenomenon might represent a protective mechanism against paf-mediated effects in thrombotic and cardiovascular diseases. This study has been presented in part as a preliminary report at the 72nd Annual Meeting of the Federation of American Societies for Experimental Biology, Las Vegas, NV, May 1988 (1).     

Molecular mobility in polycyanurate networks investigated by viscoelastic measurements and molecular simulations

The dynamic mechanical behavior of a series of polycyanurate networks has been studied in the glassy state as a function of cyanate conversion. Two relaxations, β and γ, were defined and the Arrhenius dependence and Starkweather treatments were applied. To understand the origin of these sub-T_g relaxations, molecular modeling (both mechanics and dynamics) was used on model molecules representative of the network structure. Two types of molecular motion were examined: rotation of the phenylene ring and crankshaft of the chain segment between crosslinks (i.e., triazine rings).     

A study of some alkali metal-furangraphite compounds and of their charge transfer characteristics

The reaction of furan on the 1st- to 6th-stage potassium-graphite compounds, as well as on some derivatives of other alkali metals, has been critically examined. The composition and the main structural features were determined and it is suggested that the formation of the ternary compound and the stage changes observed are intimately connected with a redistribution between the furan and the aromatic layers of the electron donated by the metal atom. The presence of the electron on the furan has two important consequences: an increase in the apparent volume of the molecules due to the fuzzy orbital occupied by the electron and to the repulsion between the charged species, and a long-term chemical instability of the ternary compound probably due to the presence of the electron on an antibonding orbital.     

BIOAVAILABILITY AND BIOACCUMULATION OF PAH IN AMPHIPODS EXPOSED TO REFERENCE AND HARBOR SEDIMENTS

The amphipods Corophium volutator collected from inter-tidal mud flats away from urbanization display the presence of phenanthrene, while larger molecular weight PAHs were only detected in sediments. The latter compounds were abundant in sieved surface sediments collected from Halifax Harbor receiving combined road runoff and sewage effluents and a smaller fraction of the contaminants were bioavailable to amphipods. In laboratory exposures, the kinetics of contaminants uptake by amphipods displayed the steepest increase in concentration the first day of exposure, continued to increase and then decreased, reaching a steady state within a week. The depuration of PAH was more than ten times slower than observed for maximum uptake. Our study indicated the important role played by feeding in the bioavailability and toxicity of sediments. The PAH fingerprint associated with the grain size of particles needs pursuing to better delineate the exposure pathway of PAH to sediment dwelling organisms.