Textile with silver silica spheres: its antimicrobial activity against <Emphasis Type="Italic">Escherichia coli and Staphylococcus aureus</Emphasis>

The aim of this study was to investigate antimicrobial activity of textiles doped with silver in different forms. Three types of textiles were prepared and examined: textiles doped with commercially available Ag nanoparticles, textiles doped with commercial colloidal silver and textiles doped with silver silica SiO₂/Ag spheres. The specimens of silica submicron spheres were synthesized by the sol–gel method as a matrix for biological active silver. The results of microbiological tests revealed that among three kinds of Ag doped textiles only these doped with SiO₂/Ag spheres are bacteriostatically active. During the experiments minimal inhibiting bacteria growth concentration of active SiO₂/Ag spheres added to textiles was determined.     

Abelian cosmic string in the extended Starobinsky model of gravity

We analyze numerically the behaviour of the solutions corresponding to an Abelian cosmic string taking into account an extension of the Starobinsky model, where the action of general relativity is replaced by \(f(R) = R - 2\Lambda + \eta R^2 + \rho R^m\), with \(m > 2\). As an interesting result, we find that the angular deficit which characterizes the cosmic string decreases as the parameters \(\eta \) and \(\rho \) increase. We also find that the cosmic horizon due to the presence of a cosmological constant is affected in such a way that it can grows or shrinks, depending on the vacuum expectation value of the scalar field and on the value of the cosmological constant.     

Self-Turbulent Flame Speeds

This paper reports an experimental investigation of premixed propane and methane-air flames propagating freely in tubes 1.5?m long and with diameters ranging from 26 to 141?mm. The thermo-acoustic instability was eliminated by means of a novel acoustic absorber placed at the closed end of the tube. We first remark that the flame can adopt different shapes either quasi-axisymmetric and normal to the mean direction of propagation, or inclined with a larger propagation speed because of the increase in flame surface area. The minima of the propagation speeds, corresponding to non-tilted flame propagation, are then analyzed using analytical models for the self-turbulent flame propagation. The concept of a cut-off wavelength appears to be relevant to explain the different behaviors observed on the rich side of methane-air and propane-air flames.     

Subsolidus phase equilibria in the system AlVO4−MoO3

The phase equilibria in the solid state in the system AlVO₄?MoO₃ were determined by DTA and XRD methods. The experimental results are presented in the form of a phase diagram. In the subsolidus area, the system AlVO₄?MoO₃ is a real two-component system only within the range AlVO₄?AlVMoO₇.     

Differentiation of positional isomers of nitro meso-tetraphenylporphyrins by tandem mass spectrometry

We studied by tandem mass spectrometry two isomers of nitro meso-tetraphenylporphyrin, one with a nitro group in the para position of a phenyl ring and the other with the same group in a beta-pyrrolic position, and their copper complexes. Collisional activation of the molecular ions of both free-base porphyrins and of their copper complexes produces an array of product ions that permit ready differentiation of the two positional isomers. The diagnostic ions, when the nitro group is in a beta-pyrrolic position, may be produced through intramolecular and double cyclization processes, triggered by the interaction of the nitro substituent with the neighboring meso-phenyl ring. These diagnostic ions do not form when the nitro group is in the para position. The gas-phase processes have precedents in solution chemistry.     

Study on the initiation step of 2-(9-carbazolyl)ethyl glycidyl ether polymerization by K, K (15-crown-5)2

Several reactions occur during the initiation of 2-(9-carbazolyl)ethyl glycidyl ether polymerization by K⁻, K⁺ (15-crown-5)₂. At first the oxirane ring is opened mainly in the β-position. An organometallic intermediate obtained cleaved then the linear ether bond in the substituent and the cyclic one in crown ether. Various potassium alkoxides are finally formed. They are the real initiators of the polymerization. 9-Vinylcarbazole being another reaction product is inactive in this process.     

Radical processes induced in poly(siloxaneurethaneureas) by ionising radiation

The effect of ionizing radiation on poly(siloxaneurethaneureas), comprising the soft phase of poly(dimethylsiloxane) chains and hard urethane segments, was examined by electron paramagnetic resonance (EPR) spectroscopy and gas chromatography (GC). It was found that radical processes in the investigated polymers were determined predominantly by polysiloxane segments. Dehydrogenation proceeded mainly in the terminal groups of dimethylsiloxane sequences, forming methylene radicals, whereas abstraction of methyl group dominated in inner fragments of the polysiloxane chain. However, upon irradiation no change in glass transition temperature of polysiloxane segments was detected by DSC.     

Structural Study of Methane Hydrate

The authors present a structural study of methane hydrate by using MP2 calculations and the QTAIM method. Two different structures are analyzed for the empty clathrate molecule. Both structures exhibit 30 hydrogen bonds and they differ in the position of the 10 O–H bonds that are not involved in hydrogen bonds. As the available space in the middle of the structure, where the guest could be located, is the same in both cases, most stable molecule is considered to be filled with methane. We also try to establish similarities and differences between methane occupied and empty units by analyzing geometrical and density charge properties, particularly what is related to the hydrogen bonds among water molecules in the clathrate. Our results allow us to conclude that the introduction of methane does not vary the main structural properties of this molecule.     

Cyclic and stripping voltammetry of Se(+4) and Se(-2) at carbon electrodes in acid solutions

The behaviour of the Se(+4)?Se(0)?Se(?2) system was studied by cyclic and stripping voltammetry using several kinds of graphite and glassy carbon electrodes in the pH range from 0 to 8. Well-defined curves of Se(+4) reduction were obtained with a very soft graphite electrode, whereas poorly defined curves were recorded with glassy carbon electrodes. The reduction of Se(+4) in acid solution led to the formation of two forms of elemental selenium. One was formed in a direct electroreduction and the other in a subsequent chemical reaction between Se(+4) and Se(?2). These two forms of Se(0) gave separate reduction and oxidation peaks. Hydrogen selenide was anodically oxidized stepwise to elemental selenium and selenous acid. With an increase of pH the extent of Se(+4) reduction decreased and the extent of Se(?2) oxidation increased.The cathodic and anodic stripping peaks of elemental selenium cannot be used for the determination of traces of Se(+4) because they appear only in solutions with Se(+4) concentrations >1×10^?5 mol 1^?1.