Multiscale vulnerability of complex networks

We present a novel approach to quantify the vulnerability of a complex network, i.e., the capacity of a graph to maintain its functional performance under random damages or malicious attacks. The proposed measure represents a multiscale evaluation of vulnerability, and makes use of combined powers of the links' betweenness. We show that the proposed approach is able to properly describe some cases for which earlier measures of vulnerability fail. The relevant applications of our method for technological network design are outlined.     

Combined kinetic analysis of thermal degradation of polymeric materials under any thermal pathway

Combined kinetic analysis has been applied for the first time to the thermal degradation of polymeric materials. The combined kinetic analysis allows the determination of the kinetic parameters from the simultaneous analysis of a set of experimental curves recorded under any thermal schedule. The method does not make any assumptions about the kinetic model or activation energy and allows analysis even when the process does not follow one of the ideal kinetic models already proposed in the literature. In the present paper the kinetics of the thermal degradation of both polytetrafluoroethylene (PTFE) and polyethylene (PE) have been analysed. It has been concluded, without previous assumptions on the kinetic model, that the thermal degradation of PTFE obeys a first order kinetic law, while the thermal degradation of PE follows a diffusion-controlled kinetic model.     

Photoluminescence in silicon/silicon oxide films produced by the Pulsed Electron Beam Ablation technique

In this work we report studies of the photoluminescence emission in samples based on Si/SiO_x films deposited by the Pulsed Electron Beam Ablation (PEBA) technique. The samples were prepared at room temperature using targets with different Si/SiO₂ concentrations. The samples were characterized using X-ray Absorption Edge Spectroscopy (XANES) at the Si―K edge, Raman spectroscopy, Photoluminescence (PL) and X-ray Photoelectron Spectroscopy (XPS). The concentration of a-Si and nc-Si in the film was dependent on the silicon concentration in the target. It was also observed that the PL is strongly dependent on the structural amorphous/crystalline arrangement.     

Effect of diluent and atmosphere on DTA peaks of decomposition reactions

A study has been carried out of the influence of sample dilution, the nature of the gas atmosphere, and the static or flowing conditions of this, on the DTA curves resulting from the thermal decomposition of solids. The results obtained seem to indicate that only the reversible reactions of solid thermal decomposition are seriously affected by such factors.

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Zusammenfassung Es wurde der Einfluß der Verdünnung der Probe, der Beschaffenheit der Gasatmosphäre und seiner statischen oder Strömungsbedingungen auf die DTA-Kurven der thermischen Zersetzung von Festkörpern untersucht. Die Ergebnisse deuten darauf hin, daß nur die reversiblen Reaktionen der thermischen Zersetzung von Festkörpern durch solche Faktoren stärker beeinflußt werden.

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Résumé On a étudié l'influence de la dilution de l'échantillon, de la nature de l'atmosphère ainsi que le fait que celle-ci soit statique ou dynamique, sur les courbes ATD résultant de la décomposition thermique des corps solides. Les résultats obtenus indiquent que de tels facteurs n'influencent de façon sérieuse que les réactions réversibles de décomposition.

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Chemistry of dithiocarbamate derivatives of amino acids. Part III. X-ray photoelectron spectroscopy of Ba(S2CNHCH2CO2)·3H2O. I.r. and e.s.r. studies of α-amino acid-dithiocarbamate complexes of copper(II)

Summary Coordination compounds [Cu(S₂CNHCHRCO₂H)₂], were obtained by reaction of dithiocarbamate derivatives of amino acids with copper(II), and the products were characterized by i.r. and e.s.r. spectroscopy. The xps spectrum of Ba(S₂CNHCH₂CO₂)·3H₂O is reported.     

Influence of particle size on the stoichiometry of chemisorption of oxygen on supported nickel catalysts

It has been found that the stoichiometry of adsorption of oxygen on nickel supported on silica is linearly correlated to the particle size of the metal. It is shown that the combined use of hydrogen and oxygen chemisorption at room temperature allows to determine both the dispersity and reduction degree of nickel.

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Kinetic Analysis of Solid State Reactions by Means of Stepwise Isothermal Analysis (SIA) and Constant Rate Thermal Analysis (CRTA) A comparative study

The results obtained in this work point out that both SIA and CRTA traces, simulated assuming the same values of the reaction rate, are identical provided that either 'n order’ or diffusion controlled kinetics are concerned. The α-T CRTA plots of solid state reactions fitting an Avrami-Erofeev kinetic model show that the temperature decreases with increasing α until reaching a minimum at a value of the reacted fraction α = αmin characteristic of the Avrami-Erofeev exponent. The shapes of the corresponding SIA diagrams are quite different and a very long isothermal step is obtained. Moreover, the reaction rate is not maintained constant during the isothermal period but it shows a maximum at a value of α depending on the Avrami-Erofeev coefficient. It is important to point out that this αmax value agrees with the corresponding αmin calculated from a CRTA curve by assuming the same Avrami-Erofeev exponent. This revised version was published online in July 2006 with corrections to the Cover Date.