Cyclodextrin‐anionic polysaccharide hydrogels: Synthesis,characterization, and interaction with some organic molecules (water pollutants,drugs, proteins)

Hydrogel microparticles have been prepared through cocrosslinking of cyclodextrin and of anionic carboxymethyl or sulfopropyl pullulan with a new bifunctional reagent: 3‐(glycidoxypropyl)trimethoxysilane. This reagent forms crosslinking both through grafting with the epoxy end on the OH polysaccharide and through hydrolysis and condensation of the methoxy silane groups from the other end. Samples of cyclodextrin/anionic polysaccharides with various amounts of crosslinking agent were prepared. Characterization of the hydrogel microparticles considered the water swelling behavior, porosity measurements, retention of biologically active substances, which can occur by their inclusion in cyclodextrin inner cavities and in the pores of hydrogels, as well as through the electrostatic forces toward anionic polyelectrolyte charges. Their improved retention of various organic molecules as water pollutants, drugs, enzymes, recommend them as chromatographic supports, supports for the separation/immobilization of enzymes or for controlled release systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Sensor deployment in wireless sensor networks with linear topology using virtual node concept

Wireless Networks - In a multi-hop wireless sensor network with a convergecast communication model, there is a high traffic accumulation in the neighborhood of the sink. This area constitutes the...     

Phase-type distributions and representations: Some results and open problems for system theory

In this paper we consider phase-type distributions. These distributions correspond to the random hitting time of an absorbing Markov chain. They are used for modelling various random times, in particular, those which appear in manufacturing systems as processing times, times to failure, repair times, etc. The Markovian nature of these distributions allows the use of very efficient matrix based computer methods for performance evaluation. In this paper we give a system theory oriented introduction to phase-type distributions. We concentrate mainly on the representation problem which consists of finding a Markov chain associated with some phase-type distribution. This is a realization problem in the sense of system theory with a lot of links with the classical linear system theory but also with a number of constraints which make the problem harder but more interesting. Indeed this problem has strong connections with the positive realization problem in control theory. The paper recalls known results, gives some new results, and points out the main remaining problems.     

The development of spatial structure in an ionic chemical system induced by applied electric fields

The spatio-temporal structures that can arise in an ionic chemical system with a cubic autocatalytic reaction step (Gray-Scott kinetics) in the presence of an applied electric field are described. A linear stability analysis of the resulting reaction-diffusion-advection system, with different diffusion coefficients and consequently different electrochemical migration rates for the reacting species, suggests the possibility of both convective structures ('DIFICI') and Turing patterns (as well as interaction between them). The detailed linear analysis determines the domain of existence of these features in parameter space, the predictions from which are confirmed by extensive numerical simulations. These reveal that a wide variety of propagating structures can be sustained by the system, depending on the electric field strength and whether the ratio of diffusion coefficients of autocatalyst and substrate is above or below the critical values for Turing bifurcations.     

Forced convective structures in a differential-flow reactor

A model of an autocatalytic reaction in a differential-flow reactor is considered in which the reactant is immobilized and the autocatalyst allowed to flow (with uniform velocity) and to diffuse. Consideration is given to the influence that a periodic external signal (fluctuations in the inflow concentration of the autocatalyst) can have upon the convective structures which exist in this model. It is shown that, depending on the frequency of the signal, there are two parameter regions giving distinct spatio-temporal responses. There is a region of high excitation waves (convected forced waves) which appear for a finite range of frequencies. Outside this range there are two domains of natural response waves. Close to the boundary of these regions there are irregular responses suggestive of an excitable system: packets of travelling waves of complex form develop which appear at non-regular intervals surrounded by small amplitude periodic waves.     

Phase-transitions in GeSb induced by customized ultrafast optical pulses

The use of ultrafast laser pulses to initiate solid-state phase-transitions in certain materials has shown promise in achieving sub-nanosecond phase changes with different optical properties. These phase changes have been well studied using pulse durations between femtoseconds and nanoseconds to determine the dynamics for the reversible phase changes on multiple time scales. In this study femtosecond pulse shaping techniques, driven by evolutionary algorithms, were used to obtain optimized temporally shaped ultrashort laser pulses to induce and control permanent phase changes in GeSb thin-films. Through monitoring the pulse effects it has been determined that the crystalline-to-amorphous phase transition is minimized using optical pulses with pulse widths less than the electron-phonon coupling time. It is maximized by using pulses longer than the time required for energy transfer from the excited carriers to the lattice.     

Dielectric and tunability properties of La-doped BaTiO3 ceramics

La-doped BaTiO₃ (x = 0.001; 0.0025; 0.005; 0.01; 0.025) ceramics were prepared via conventional solid state reaction and sintered at 1300 °C for 6 h, resulting in dense single phase ceramics with homogeneous microstructures. The temperature dependence of dielectric permittivity of the ceramics has been investigated. The results show a decrease of T_C with lanthanum addition. The degree of diffuseness of phase transition is more pronounced for high La content, implying the existence of a composition-induced phase transition of the ceramics. The dc-tunability at room temperature was investigated and experimental data were discussed in terms of the Johnson model completed with a Langevin term that describes “extrinsic” contribution to the non-linear ?(E) dependences.     

Effects of geometrical dimensions of flow channels of a large-active-area PEM fuel cell: A CFD study

Various flow field designs have been numerically investigated to evaluate the effect of pattern and the cross-sectional dimensions of the channel on the performance of a large active area PEM fuel cell. Three types of multiple-serpentine channels (7-channels, 11-channels and 14-channels) have been chosen for the 200 cm² fuel cell investigated and numerically analysed by varying the width and the land of the channel. The CFD simulations showed that as the channel width decreases, as in the 14-channels serpentine case, the performance improves, especially at high current densities where the concentration losses are dominant. The optimum configuration, i.e. the 14-channels serpentine, has been manufactured and tested experimentally and a very good agreement between the experimental and modelling data was achieved. 4 channel depths have been considered (0.25, 0.4, 0.6 and 0.8 mm) in the CFD study to determine the effects on the pressure drop and water content. Up to 7% increase in the maximum reported current density has been achieved for the smallest depth and this due to the better removal of excess liquid water and better humidification of the membrane. Also, the influence of the air flow rate has been evaluated; the current density at 0.6 V increased by around 25% when air flow rate was increased 4 times; this is attributed to better removal of excess liquid water.     

Antimicrobial Properties of TiO2 Microparticles Coated with Ca- and Cu-Based Composite Layers

The ability of TiO₂ to generate reactive oxygen species under UV radiation makes it an efficient candidate in antimicrobial studies. In this context, the preparation of TiO₂ microparticles coated with Ca- and Cu-based composite layers over which Cu(II), Cu(I), and Cu(0) species were identified is presented here. The obtained materials were characterized by a wide range of analytical methods, such as X-ray diffraction, electron microscopy (TEM, SEM), X-ray photoelectron (XPS), and UV-VIS spectroscopy. The antimicrobial efficiency was evaluated using qualitative and quantitative standard methods and standard clinical microbial strains. A significant aspect of this composite is that the antimicrobial properties were evidenced both in the presence and absence of the light, as result of competition between photo and electrical effects. However, the antibacterial effect was similar in darkness and light for all samples. Because no photocatalytic properties were found in the absence of copper, the results sustain the antibacterial effect of the electric field (generated by the electrostatic potential of the composite layer) both under the dark and in light conditions. In this way, the composite layers supported on the TiO₂ microparticles’ surface can offer continuous antibacterial protection and do not require the presence of a permanent light source for activation. However, the antimicrobial effect in the dark is more significant and is considered to be the result of the electric field effect generated on the composite layer.