Analysis of phenol-formaldehyde resols by gel permeation chromatography

The chromatographic analysis of resol solutions in tetrahydrofuran solvent, by means of a set of columns packed with crosslinked polystyrene gels, has been carried out with adequate resolving power for a clear-cut qualitative or semiquantitative differentiation between various types of resols to be practicable. The resulting chromatograms, which show the distribution of different constituents by molecular size, could be interpreted by the use of reference substance and by calibrating the system with a number of compounds of known structures. The method has been used to investigate the way in which various reaction parameters (nature of catalysts, proportion of starting material, treatments undergone by the resols) affect the composition of resols. Different commercial products have been thus characterized. It has also afforded an insight into the progress of the polycondensation reaction as a function of time and helped to state the reactivity of different groups and unblocked ring positions. Thus, an hydroxymethyl group appears to be more reactive in the para than in the ortho position. Otherwise the reactivity of unblocked ring positions would be enhanced by an hydroxymethyl group in the ortho rather than para position.     

Existence de quatre types de sites reactionnels dans l'oxydation du graphite

We have studied the temperature programmed decomposition of graphite-oxygen surface complexes using a gas flow apparatus under atmospheric pressure with infrared CO and CO₂ detection. We have shown that the oxygen is chemisorbed on four types of sites forming surface complexes which on decomposition give mainly CO and some CO₂. The first two types of sites, A and B, are formed by ‘labile’ carbon atoms created during the degassing carried out prior to each experiment. These two types of sites disappear without reconstitution upon desorption of the complexes. The other two, C and D, are formed by edge carbon atoms, normally linked to other atoms in the graphite lattice. The C type sites form by oxidation only at temperatures below about 950°C and give rise to hexagonal pits with sides oriented in the (101?0) crystallographic direction (‘arm-chair’ configuration). The D type sites form at temperatures above about 950°C and give rise to hexagonal pits oriented in the (11?20) crystallographic direction (‘zig-zag’ configuration). Water inhibits the formation of oxygen surface complexes on the C sites and it may be considered that it is essentially on these sites that the water is chemisorbed.     

A Decade of Oxothiomolybdenum Wheels: Synthesis,Behavior in Solution,and Electrocatalytic Properties

The last decade has see the development of sulfur-containing polyoxometalates (POTMs) as a subclass of the polyoxometalate family. The structural and physico-chemical properties of this emerging class of compounds is dominating by the striking coordination properties of the [Mo₂O₂S₂(OH₂)₆]²⁺ oxothio cation, used as a building block. The cyclic topology of this arrangement corresponds to the main feature of the {Mo₂O₂S₂}-based compounds, able to develop cycle-based chemistry. The control of the linear oligomerization of the {Mo₂O₂S₂} core is achieved by the presence of the anionic component, which acts as a template. Here, we report on recent examples which illustrate how the use of various template ions such as halide, sulfate, polyphosphate, and polycarboxylate anions allows to tune the nuclearity of the inorganic host from {Mo₈} to {Mo₁₈}. A special focus on behavior in solution is given, highlighting the dynamic and fluxional character of these host–guest systems. The Diffusion Ordered Spectroscopy (DOSY) ¹H NMR, carried out on a large series of cycle-based and capsule-like compounds, demonstrates that such a method can be applied for the speciation of POM anions in solution. Finally, electrocatalytic behavior of the {Mo₂O₂S₂}-based compounds is presented. Preliminary results show that the electrocatalytic reduction of protons into hydrogen (HER) could constitute one of the most relevant applications for this class of molecular compounds.     

Effect of physical aging on nano- and macroscopic properties of poly(methyl methacrylate) glass

Physical aging of amorphous poly(methyl methacrylate) has been studied by low frequency Raman scattering, broad-band dielectric spectroscopy, low frequency high resolution mechanical spectroscopy and differential scanning calorimetry. The material was subjected to different thermal histories by isothermal aging. A consistent relationship between the changes caused by the physical aging in nanostructure and molecular dynamics has been found. The aging makes the structure more homogeneous at a scale of few nanometers, bringing it to a structural state of lower energy. These structural changes affect mainly the -relaxation, however, some increase in the relaxation strength as well as an increase in the activation energy of the β-relaxation is also observed.     

Preparation of zeolite filled glassy polymer membranes

The incorporation of zeolite particles in the micrometer range into polymeric matrices was investigated as a way to improve the gas separation properties of the polymer materials used in the form of membranes. The adhesion between the polymer phase and the external surface of the particles appeared to be a major problem in the preparation of such membranes when the polymer is in the glassy state at room temperature. Various methods were investigated to improve the internal membrane structure, that is, surface modification of the zeolite external surface, preparation above the glass-transition temperature, and heat treatment. Improved structures were obtained as observed by scanning electron microscopy, but the influence on the gas separation properties was not in agreement with the observed structural improvements. © 1994 John Wiley & Sons, Inc.     

MISR prelaunch instrument calibration and characterization results

Each of the nine cameras that compose the Multi-angle Imaging SpectroRadiometer (MISR) has been rigorously tested, characterized, and calibrated. Requirements on these tests include a 3% (1σ) radiometric calibration requirement, spectral response function determination of both the in- and out-of-band regions, and distortion mapping. The latter test determines the relative look-angle to the ground corresponding to each focal plane detector element. This is established to within one-tenth of the instantaneous field-of-view. Most of the performance testing was done on the cameras as they completed assembly. This was done to take advantage of the serial delivery of the hardware, minimize the required size of the thermal-vacuum facilities, and allow testing to occur early in the schedule allocated for the hardware build. This proved to be an effective strategy, as each of the test objectives was met. Additional testing as an integrated instrument included verification of the data packetization, camera pointing, and clearances of the fields-of-view. Results of these studies have shown that the MISR cameras are of high quality and will meet the needs of the MISR science community. Highly accurate calibration data are on-hand and available for conversion of camera output to radiances     

Species identification of meat products by ELISA

ELISA methods used in this study are proved to detect low contents of animal species (pork, beef, sheep and poultry), even in highly processed foods. They present the advantages of being robust, cheap and easy to perform. Nevertheless, F factors, determining the threshold values of the test, need to be validated for each species.     

Influence of the sampling area of the stem on the mechanical properties of hemp fibers

Natural fibers appear to be a promising alternative to glass fibers for the reinforcement of polymer matrix composites. However, the wide dispersion of their mechanical properties slows down their development.The aim of this study was to evaluate the influence of the sampling area of the stem on the mechanical properties of hemp fibers. Tensile tests were carried out on fibers extracted from the bottom, the middle, and the top of one stem. The results show there is only slight variations between the different areas: fibers from the middle exhibit higher tensile strength and ultimate elongation than top and bottom fibers, but there are no differences in terms of stiffness. A strong dependence of the fiber mechanical properties on their diameter is observed. This dependence induces more dispersion of the properties than the sampling area, thus it seems relevant to consider the whole stem to extract fibers, without defining distinct areas.     

Development, application and comparison of an enzyme immunoassay and a high-performance liquid chromatography method for the determination of the aromatase inhibitor CGS 20,267 in biological fluids

CGS 20,267 is a new potent and selective, nonsteroidal, oral aromatase inhibitor. For its determination in human plasma and urine, an enzyme immunoassay (EIA) and an HPLC method were developed. The EIA showed good precision and accuracy (intra- and interassay variation between 3.0 and 17.7%, recoveries between 81 and 106%) and a quantitation limit of 0.7 nmol/L. A strong cross reactivity of the antibodies with the hydroxy metabolite of CGS 20,267 (CGP 44,645) was observed. The HPLC method showed a quantitation limit in plasma of 28 and 34 nmol/L for CGS 20,267 and CGP 44,645, respectively. For urine, concentrations down to 180 nmol/L (CGS 20,267) and 210 nmol/L (CGP 44,645) could be measured. A cross check between EIA and HPLC on plasma samples from healthy male volunteers or breast cancer patients treated orally with CGS 20,267 revealed an excellent correlation (slope = 0.934, intercept = 26, r = 0.991). However, the EIA measurements of urine samples yielded 3-25 times higher concentrations than those obtained by HPLC. Further, HPLC analysis revealed the presence of CGS 20,267 and cross-reacting metabolites in urine but not in plasma. Therefore, the EIA can only be used for the determination of CGS 20,267 in plasma samples.     

Self-awareness, probability of improvement, and the self-serving bias.

Evidence for the self-serving bias (attributing success internally and failure externally) is inconsistent. Although internal success attributions are consistently found, researchers find both internal and external attributions for failure. The authors explain these disparate effects by considering the intersection of 2 systems, a system comparing self against standards and a causal attribution system. It was predicted that success and failure attributions are moderated by self-awareness and by the ability to improve. When self-focus is high (a) success is attributed internally, (b) failure is attributed internally when people can improve, (c) failure is attributed externally when people cannot improve, and (d) these attributions affect state self-esteem. Implications for the self-serving bias are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)