A SAXS study of kinetics of aggregation of TEOS-derived sonogels at different temperatures

The kinetics of aggregation of tetraethoxysilane (TEOS)-derived silica sols, produced by acid-catalyzed and ultrasound-stimulated hydrolysis, were studied by 'in situ' measurements of small-angle X-ray scattering (SAXS) at the temperatures 40 degreesC, 60 degreesC and 70 degreesC. The results were analyzed in terms of the evolution with time (t) of the SAXS intensity probing the mass fractal characteristics of the system, the average radius of gyration (Rc,) of the clusters and the number of primary particles per cluster. The aggregation process yields mass fractal structures which exhibit a scattering exponent (alpha) practically equal to 2, in the probed length scale range (5.3 nm < 1/q < 0.22 nm), beneath and even far beyond the gel point. This suggests that a is a direct measure of the real mass fractal dimension (D) of the structure. The precursor sol (pH = 2) exhibits I nm mean sized clusters with mass fractal dimension D similar to 1.9. Increasing the pH to 4.5, the cluster mean size and the number of primary particles per cluster increase but the system keeps a more opened structure (D similar to 1.4). In the first aggregation stages, D increases up to similar to2 by incorporating primary particles to the clusters without changing their mean size. From this stage, the aggregation progresses following a thermally activated scaling law well described by R-G similar tot(1/D) in all cases. This is indicative of a diffusion-controlled cluster-cluster aggregation process. The activation energy of the process was found to be 91.7 kJ/mol. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Use of spin label EPR spectra to monitor peptide chain aggregation inside resin beads.

An EPR approach to monitor peptide chain aggregation inside resin beads is introduced. Model low and highly peptide-loaded resins containing an aggregating sequence were labeled with a paramagnetic amino acid derivative and studied with regard to their solvation behavior in different solvent systems. For the first time in the peptide synthesis, EPR spectroscopic has allowed the detection of differentiated levels of peptide chain aggregation as a function of solvent and resin loading. (C) 1997, Elsevier B.V. Ltd. All rights reserved.

Adsorption processes in layer-by-layer films of poly(o-methoxyaniline): the role of aggregation

In this work we investigate the effect from the solution concentration on aggregation in layer-by-layer (LBL) films of poly(omethoxyaniline) (POMA) alternated with poly(vinyl sulfonic acid). Films are adsorbed on hydrophilized glass substrates and characterized with UV-Vis spectroscopy and atomic force microscopy. The formation of aggregates is favored in more concentrated solutions, leading to an increase in the diameter of the domains. This is caused by stronger polymer-polymer interactions under high concentrations. The size of POMA aggregates in solution is estimated to be larger than in LBL films, which is surprising because one should expect aggregates from solution to coalesce into larger aggregates in the deposited films. This unexpected result may be explained by a swelling effect of aggregates in the aqueous POMA solutions, consistent with other reports in the literature which consider the aggregates in solution to be made up of smaller aggregates. Upon adsorption on a solid substrate to form the LBL film, a molecular reorganization probably takes place, resulting in smaller aggregates. It is also found that the size distribution of the POMA domains in the LBL films is determined by the concentration of the solution. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Aggregation-based decomposition for multi-divisional models

The aggregation theory of mathematical programming is used to study decentralization in convex programming models. A two-level organization is considered and a aggregation-disaggregation scheme is applied to such a divisionally organized enterprise. In contrast to the known aggregation techniques, where the decision variables/production planes are aggregated, it is proposed to aggregate resources allocated by the central planning department among the divisions. This approach results in a decomposition procedure, in which the central unit has no optimization problem to solve and should only average local information provided by the divisions.

Perioperative administration of vedaprofen, tramadol or their combination does not interfere with platelet aggregation, bleeding time and biochemical variables in cats

A randomized double blind and placebo controlled design was used to investigate the hemostatic, biochemical, gastrointestinal and behavioral effects of pre- and postoperative administration of vedaprofen 0.5 mg/kg PO (V), tramadol 2 mg/kg SC (T), their association (VT) or placebo (P) in 40 adult female cats (3.0 +/- 0.32 kg; 1.8 +/- 0.7 years) distributed in groups of 10. Platelet aggregation and bleeding time were measured before and 52 11 after ovariohysterectomy. Serum urea, creatinine, alanine aminotransferase, alkaline phosphatase and gamma-glutamyl transferase concentrations were measured before and 7 days postoperatively. The occurrence of vomiting, frequency and consistency of feces, and behavior were observed for 7 days postoperatively. Morphine (0.5 mg/kg, IM) was used as rescue analgesic. Laboratory variables did not change. Vomiting was observed only after morphine administration. Mild euphoria was observed in T and VT. The perioperative use of vedaprofen and/or tramadol did not modify the hemostatic, biochemical and gastrointestinal function in cats. (C) 2009 ESFM and AAFP. published by Elsevier Ltd. All rights reserved.