PMMA‐modified divinylester/styrene resins: Phase diagrams and morphologies

Binary and ternary experimental cloud‐point curves (CPCs) for systems formulated with a low molar mass synthesized divinylester (DVE) resin, styrene (St), and poly(methyl methacrylate) (PMMA) were determined. The CPCs results were analyzed with the Flory–Huggins (F‐H) thermodynamic model taking into account the polydispersity of the DVE and PMMA components, to calculate the different binary interaction parameters and their temperature dependences. The St‐DVE system is miscible in all the composition range and down to the crystallization temperature of the St; therefore, the interaction parameter expression reported for a higher molar mass DVE was adapted. The interaction parameters obtained were used to calculate the phase diagrams of the St‐PMMA and the DVE‐PMMA binary systems and that of the St‐DVE‐PMMA ternary system at three different temperatures. Quasiternary phase diagrams show liquid–liquid partial miscibility of the St‐PMMA and DVE‐PMMA pairs. At room temperature, the St‐DVE‐PMMA system is miscible at all compositions. Final morphologies of PMMA‐modified cured St‐DVE materials were generated by polymerization‐induced phase separation (PIPS) mechanism from initial homogeneous mixtures. SEM and TEM micrographs were obtained to analyze the generated final morphologies, which showed a direct correlation with the initial miscibility of the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4539–4549, 2006     

Hybrid Photopatterned Enzymatic Reaction (HyPER) for in Situ Cell Manipulation

The ability to design artificial extracellular matrices as cell‐instructive scaffolds has opened the door to technologies capable of studying the fate of cells in vitro and to guiding tissue repair in vivo. One main component of the design of artificial extracellular matrices is the incorporation of biochemical cues to guide cell phenotype and multicellular organization. The extracellular matrix (ECM) is composed of a heterogeneous mixture of proteins that present a variety of spatially discrete signals to residing cell populations. In contrast, most engineered ECMs do not mimic this heterogeneity. In recent years, photo‐deprotection has been used to spatially immobilize signals. However, this approach has been limited mostly to small peptides. Here we combine photo‐deprotection with enzymatic reaction to achieve spatially controlled immobilization of active bioactive signals that range from small molecules to large proteins. A peptide substrate for transglutaminase factor XIII (FXIIIa) was caged with a photo‐deprotectable group, which was then immobilized to the bulk of a cell‐compatible hydrogel. With focused light, the substrate can be deprotected and used to immobilize patterned bioactive signals. This approach offers an innovative strategy to immobilize delicate bioactive signals, such as growth factors, without loss of activity and enables in situ cell manipulation of encapsulated cells.     

Escherichia vulneris infection. Report of 2 cases

BACKGROUND: Escherichia vulneris is an enterobacteriaceae seldom isolated in microbiology laboratories. We report two cases of infection with positive cultures for this microorganism. METHODS: Microbiological cultures of wound secretion and peritoneal fluid on usual media. Identification by PASCO and API 20E systems. Antimicrobial sensitivity was performed by a commercial microdilution system. RESULTS: The first case is a postsurgical hand infection from which was isolated Escherichia vulneris with Enterococcus faecium, it shows the typical presentation of infection by this bacteria. The second case consists of a peritonitis after aggressive abdominal surgery. In the peritoneal fluid culture, Escherichia vulneris and Cedecea neteri were recovered. CONCLUSIONS: The isolation of Escherichia vulneris has not been reported previously in Spain. We contribute towards its better knowledge with two clinical reports: a typical infection and an exceptional isolation from peritoneal fluid.     

A COMPLEX CASE-BASED ADVISOR

The complexity of current organization systems, and the increase in the importance of the realization of internal controls in firms, make it necessary to construct models that automate and facilitate the work of auditors. A tool for the decision support process has been developed. The objective of the system is to facilitate the process of internal auditing in small and medium-sized enterprises. The system analyzes the data that characterizes each one of the activities carried out by the firm, then determines the state of each activity, calculates the associated risk, detects the erroneous processes, and generates recommendations to improve these processes. The developed model is composed of two case-based reasoning systems. One is used to identify the activities that may be improved and the other to determine how the activities could be improved. Each of the two subsystems use a different problem-solving method in each of the steps of the reasoning cycle. The system has been tested in 22 small and medium-sized companies in the textile sector, located in the northwest of Spain during the last 38 months and the obtained results are very encouraging.     

On the curing kinetics of unsaturated polyesters with styrene

The curing kinetics of a general purpose unsaturated polyester (UP) with styrene was studied by differential scanning calorimetry and dielectric capacitance measurements. Benzoyl peroxide was used as initiator. Results showed that there is a complete change in the phenomenological kinetics, in different temperature ranges. At low temperatures (70–90°C), the rate went through a maximum and then showed a first-order decay. At high temperatures (100–160°C) a second-order kinetics was suitable for all the conversion range. At T > 160°C another mechanism took place when the initiator amount was less than a critical value. From the changes in the dielectric capacitance it was inferred that the conversion rate of UP unsaturations followed a first-order decay after a certain conversion, with an activation energy close to values reported for diffusion of UP radicals. Possible free radical mechanisms accounting for experimental observations are discussed.     

(CO2 + 2‐propanol) mixture as a foaming agent for polystyrene: A simple thermodynamic model for the high pressure VLE‐phase diagrams taking into account the foam vitrification

The equation of state model developed by Lacombe and Sanchez (J Phys Chem 1976, 80, 2352) is used in the form proposed later by Sanchez and Stone (Polymer Blends, Vol. 1: Formulation, 2000; Chapter 2) to correlate experimental vapor‐liquid equilibrium (VLE) data for the three binaries and the ternary systems. Experimental data from the binary systems carbon dioxide‐isopropyl alcohol (CO₂‐IPrOH), isopropyl alcohol‐polystyrene (IPrOH‐PS), and carbon dioxide‐polystyrene (CO₂‐PS) are used to calculate VLE properties for the ternary system CO₂‐IPrOH‐PS. Two‐dimensional VLE‐phase diagrams were calculated and used to describe from a thermodynamic point of view the pressure, volume, and temperature values that characterize a thermoplastic foam evolution process, from the extruder to the foaming die. For different initial mixture CO₂ + IPrOH concentrations, pressure reduction produces liquid foaming until the vitrification curve arrests the final foam volume expansion. The dependence of the vitreous transition with the system CO₂ + IPrOH concentration while foaming is represented by the Chow (Macromolecules 1980, 13, 362) equation. The calculation procedure is proposed as a design tool to reduce the amount of experimental data usually needed as a requirement previous to the design stage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2663–2671, 2007     

An HMM-based over-sampling technique to improve text classification

This paper presents a novel over-sampling method based on document content to handle the class imbalance problem in text classification. The new technique, COS-HMM (Content-based Over-Sampling HMM), includes an HMM that is trained with a corpus in order to create new samples according to current documents. The HMM is treated as a document generator which can produce synthetical instances formed on what it was trained with.To demonstrate its achievement, COS-HMM is tested with a Support Vector Machine (SVM) in two medical documental corpora (OHSUMED and TREC Genomics), and is then compared with the Random Over-Sampling (ROS) and SMOTE techniques. Results suggest that the application of over-sampling strategies increases the global performance of the SVM to classify documents. Based on the empirical and statistical studies, the new method clearly outperforms the baseline method (ROS), and offers a greater performance than SMOTE in the majority of tested cases.     

A Reinforcement Learning Algorithm in Cooperative Multi-Robot Domains

Reinforcement learning has been widely applied to solve a diverse set of learning tasks, from board games to robot behaviours. In some of them, results have been very successful, but some tasks present several characteristics that make the application of reinforcement learning harder to define. One of these areas is multi-robot learning, which has two important problems. The first is credit assignment, or how to define the reinforcement signal to each robot belonging to a cooperative team depending on the results achieved by the whole team. The second one is working with large domains, where the amount of data can be large and different in each moment of a learning step. This paper studies both issues in a multi-robot environment, showing that introducing domain knowledge and machine learning algorithms can be combined to achieve successful cooperative behaviours.