A variational view at the time-dependent minimal surface equation

We present a global variational approach to the L ²-gradient flow of the area functional of cartesian surfaces through the study of the so-called weighted energy-dissipation (WED) functional. In particular, we prove a relaxation result which allows us to show that minimizers of the WED converge in a quantitatively prescribed way to gradient-flow trajectories of the relaxed area functional. The result is then extended to general parabolic quasilinear equations arising as gradient flows of convex functionals with linear growth.     

Small size TiO2 nanoparticles prepared by laser ablation in water

Titanium dioxide nanoparticles in distilled H₂O solvent were prepared by laser ablation. The experiments were performed irradiating a Ti target with a second harmonic (532 nm) output of a Nd:YAG laser varying the operative fluence between 1 and 10 J cm⁻² and for an ablation time ranging from 10 to 30 min. Electron microscopy measurements have evidenced the predominant presence of nanoparticles with diameter smaller than 10 nm together with agglomerations of 100-200 nm whose content increases with the laser fluence. At low laser fluence the particles’ size distribution shows that more than 85% of the nanoparticles have a size smaller than 5 nm while at mid and high fluences the presence of 5-7 nm nanoparticles is predominant. XPS analysis has revealed the presence of different titanium suboxide phases with the prevalence of Ti-O bonds from TiO₂ species. The optical bandgap values, determined by UV-vis absorption measurements, are compatible with the anatase phase.     

Liquid-Phase Selective Oxidation of Propane on Silica-Supported Nafion Catalysts

The liquid-phase partial oxidation of propane in the presence of the Fen+/H2O2 Fenton system at 70℃ and 1.4 atm on silica supported Nafion catalysts has been investigated. The reaction proceeds via a radical reaction path the efficiency of which is improved by silica-supported Nafion catalysts. Because of the direct relationship between reaction rate and concentration of sulphonic acid sites of Nafion catalysts, it is inferred that the active phase enahnces the kinetics of propane conversion by promoting the rate of active radicals generation.     

PMA capped silver nanoparticles produced by UV-enhanced chemical process

An UV-enhanced single-step chemical bath process has been defined to produce precisely tailored colloidal solutions of silver nanoparticles capped with poly(methacrylic acid) (PMA) for bio-technological and packaging applications. The influence of the main process parameters on the nanoparticles chemical and structural characteristics, as well as on the reactions involved in the nanoparticle growth and polymer cross-linking, has been examined in details. A clear distinction between nanoparticle nucleation and growth, mediated by the available polymer functional groups and steric properties, has allowed to set up an effective controllable process and to obtain the desired colloids. The proper choice of the process parameters has led to a silver nanoparticles size smaller than 20 nm with a distribution peaked at less than 10 nm and stable over a period of one month.     

Temperature effects in ultrasonically activated chemical reactions

Summary The temperature effects on the yield of a sonoactivated model reaction has been investigated, to establish the role played by some physical parameters in determining either the resonant conditions for ultrasonic cavitation as well as the related enhancement of reaction rate in sonochemistry. It has been found that the statical pressure at which the resonant phenomena occur increases straightly with temperature and is related to the ?resonant volume? of the cavitating bubbles, at a given frequency of the ultrasounds. Comparison with our previous results confirms the possibility of driving the liquid-phase reacting system into resonant conditions, by varying the static pressure and/or the temperature, thus increasing the reaction rate and yield of the model chemical reaction chosen,i.e. the KMnO₄ oxidation of indane to indan-1-one.     

The effect of the composition on the properties ofγ-irradiated ethylenevinyl alcohol copolymers

Two ethylene-vinyl alcohol copolymers (Eval E and Eval F with about 45% and 25% of ethylene respectively) have been irradiated in air in the dose range 0–200 Mrad. The irradiated samples show both crosslinking and degradation; the former effect is more relevant in the copolymer with a larger content of polyethylene. Calorimetric results show that both the crystalline and the amorphous phases are involved in the reactions initiated by the irradiation.     

Synthesis and characterization of water-swellableα,β-polyasparthydrazide derivatives

, -polyasparthydrazide (PAHy) was crosslinked by glutaraldehyde to form water-swellable materials possessing a three-dimensional molecular network. Different crosslinking degrees were prepared varying glutaraldehyde/PAHy ratio and samples containing 5-fluorouracil were obtained by incorporating the drug into the polymer networks during the crosslinking reaction. All samples were characterized by swelling tests, thermal, x-ray and SEM analysis. Their microstructure was observed through scanning electron microscopy. Furthermore, for samples containing the anticancer drug,in vitro release studies were performed in pH 7.4 buffer solution.     

Synthesis and characterization of water-swellableα,β-polyasparthydrazide derivatives

The synthesis of a new crosslinked polymer by reaction of , -polyasparthydrazide and glutaraldehyde is reported. Different crosslinking degrees were obtained by varying the ratio between the aldehyde and the starting polymer. The crosslinked polymer was characterized by water swelling tests and thermal analysis. In particular, the crosslinking density and its effects on the glass transition temperature of the material were studied. Finally, the microstructure of the obtained polymer was observed using scanning electron microscopy.