A Structured Way to Use Channels for Communication in X-Machine Systems

This paper presents a new model for passing messages in communicating stream X-machine systems (CSXMS). The components are stream X-machines with ε-transitions, acting simultaneously. The states are partitioned into processing and communicating states. Passing messages between the X-machines involves only communicating states. A communication matrix is used as a common memory. It is shown that a structured way of using channels, namely via select constructs with guarded alternatives and terminate clause, may be implemented. An automatic scheme for writing concurrent programs in an Ada-like style, starting from a CSXMS, is proposed. Received December 1999 / Accepted in revised form January 2001     

Synthesis and characterization of hydrogels based on gamma irradiation of acrylic acid and methacrylic acid

In this work, hydrogels based on different ratios of acrylic acid (AAc) and methacrylic acid (MAc) monomers were prepared by gamma radiation copolymerization. The hydrogels were characterized by IR spectroscopy and thermogravimetric analysis (TGA). The effect of temperature and pH on the degree of swelling of AAc/MAc hydrogels was also studied. The results showed that the gel fraction of AAc is relatively higher than MAc, while the gel fraction of AAc/MAc hydrogels decreased slightly with increasing the ratio of MAc monomer in the initial solution. The IR spectroscopic analysis indicates the formation of copolymer networks and the presence of hydrogen bonding. The thermal study showed that PAAc hydrogel displayed higher thermal stability than PMAc and AAc/MAc hydrogels, over the studied compositions. The results showed that PAAc hydrogel reached equilibrium swelling state in water after 4 h, whereas PMAc and AAc/MAc hydrogels reached the equilibrium after 7 h. In this regard, AAc/MAc hydrogels showed degree of swelling in water lower than PAAc and higher than PMAc hydrogels. It was found that the swelling of the hydrogels based on AAc and MAc monomers or their copolymers increases with increasing temperature up to 50°C. Moreover, it was observed that the degree of swelling of hydrogels were not affected by increasing the pH values up to 4 and increased greatly within the pH values from 5 to 9. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

On the viscoelastic behaviour of a porous saturated medium

The present paper presents an example of macroscopic constitutive equation obtained from the microscopic known equations, in the case of a mixture formed by a viscoelastic solid with a viscous fluid. The effective stress appears as a consequence of the average method and not of the equation of motion. The interaction force between the constituents may be obtained directly.     

On the thermodynamic theory of mixtures

The present paper presents an axiomatic theory of mixtures which shows that a number of assumptions usually accepted in these theories are not necessary. Using an average method for passing from the microscopic level to the macroscopic one, it is deduced the system of equations of balance and the entropy inequality. The restriction imposed on the constitutive equations by the Clausius-Duhem inequality are studied.     

Nanoscale current imaging of the conducting channels in proton exchange membrane fuel cells

The electrochemically active area of a proton exchange membrane fuel cell (PEMFC) is investigated using conductive probe atomic force microscopy (CP-AFM). A platinum-coated AFM tip is used as a nanoscale cathode in an operating PEMFC. We present results that show highly inhomogeneous distributions of conductive surface domains at several length scales. At length scales on the order of the aqueous domains of the membrane, approximately 50 nm, we observe single channel electrochemistry. I-V curves for single conducting channels are obtained, which yield insight into the nature of conductive regions across the PEM. In addition, we demonstrate a new characterization technique, phase current correlation microscopy, which gives a direct measure of the electrochemical activity for each aqueous domain. This shows that a large number ( approximately 60%) of the aqueous domains present at the surface of an operating Nafion membrane are inactive. We attribute this to a combination of limited aqueous domain connectivity and catalyst accessibility.     

Superporous collagen‐sericin scaffolds

Superporous materials based on two proteins, collagen and sericin were synthesized by freeze‐drying considering various ratios between the two proteins. To evaluate the influence of sericin content on the structure/properties relationship, the obtained scaffolds were further characterized using spectroscopic analysis, thermal, and mechanical techniques. Scanning electron microscopy was used to investigate the morphological structure of the scaffolds and the swelling properties as well as the stability of the scaffolds were also assessed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Design of New Camelina Oil‐Based Hydrophilic Monomers for Novel Polymeric Materials

Triglyceride‐based monomers represent a competitive alternative to petrochemical resources in the macromolecular compounds area. In the current study, several types of hydrophilic camelina oil (CO)‐based monomers were synthesized using tunable experimental protocols that involve three different steps: first—conversion of the double bonds into epoxy rings, second—partial opening of the epoxy rings and methacrylic groups grafting and last—opening of the unreacted epoxy rings and hydrophilic units attaching. 1H‐NMR, 13C‐NMR and FTIR spectroscopy demonstrate the success of the CO functionalization with polymerizable and hydrophilic moieties—polyethylene glycol units—with different molecular weights, exhibiting self‐emulsifiable properties. Several bulk and emulsion polymerization tests were performed for the synthesized monomers and their ability to build polymer networks using different photo‐chemical procedures (using visible and UV radiations respectively) was demonstrated, without additional surfactants. FTIR spectroscopy indicates the polymerization success by the disappearance of the specific bands assigned to the double bonds from methacrylic groups and thermogravimetric analysis demonstrates that the emulsion polymerization leads to materials with an improved thermostability.     

Development of New Collagen/Clay Composite Biomaterials

The fabrication of collagen-based biomaterials for skin regeneration offers various challenges for tissue engineers. The purpose of this study was to obtain a novel series of composite biomaterials based on collagen and several types of clays. In order to investigate the influence of clay type on drug release behavior, the obtained collagen-based composite materials were further loaded with gentamicin. Physiochemical and biological analyses were performed to analyze the obtained nanocomposite materials after nanoclay embedding. Infrared spectra confirmed the inclusion of clay in the collagen polymeric matrix without any denaturation of triple helical conformation. All the composite samples revealed a slight change in the 2-theta values pointing toward a homogenous distribution of clay layers inside the collagen matrix with the obtaining of mainly intercalated collagen-clay structures, according X-ray diffraction analyses. The porosity of collagen/clay composite biomaterials varied depending on clay nanoparticles sort. Thermo-mechanical analyses indicated enhanced thermal and mechanical features for collagen composites as compared with neat type II collagen matrix. Biodegradation findings were supported by swelling studies, which indicated a more crosslinked structure due additional H bonding brought on by nanoclays. The biology tests demonstrated the influence of clay type on cellular viability but also on the antimicrobial behavior of composite scaffolds. All nanocomposite samples presented a delayed gentamicin release when compared with the collagen-gentamicin sample. The obtained results highlighted the importance of clay type selection as this affects the performances of the collagen-based composites as promising biomaterials for future applications in the biomedical field.     

Synthesis and characterization of hydroxyethyl methacrylate/acrylamide responsive hydrogels

Hydrogels based on an aqueous solution of hydroxyethyl methacrylate (HEMA) and acrylamide (AM) in the presence of trithioglycolic acid (TTGA) were prepared under the effect of gamma irradiation. These hydrogels were characterized by IR spectroscopy and thermogravimetric analysis and investigated for temperature‐ and pH‐responsive materials. It was found that TTGA is essential for the formation of HEMA/AM hydrogels at different compositions, in which the gel fraction depends on composition. A binary mixture of HEMA and AM at equal ratios was the critical composition that forms hydrogels, even in the presence of TTGA. The IR spectroscopic analysis showed that the formation of hydrogels depends on hydrogen bonding and crosslinking. The TGA investigations with respect to mass loss and the temperatures of the maximum value of the rate of reaction showed that HEMA/AM hydrogels possess higher thermal stability than that of pure HEMA and this stability increases with increasing ratio of the AM component. Also, it was observed that the temperature of the maximum value of the rate of thermal decomposition reaction depends on hydrogel composition. However, calculations of the activation energy showed that the hydrogel composed of 90% HEMA and 10% AM exhibits the highest thermal stability during the increasing or decreasing rate of reaction. Kinetic studies of swelling in water showed that HEMA/AM hydrogels displayed a temperature‐responsive character within the temperature range 25–30°C, and showed a stepwise swelling behavior in the pH range 2–10, depending on composition. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1105–1115, 2005