Remarks on the suitability of Chatterjee's method for the kinetic analysis of TG traces

It is shown that Chatterjee's method cannot be used at all to determine the value ofn in reactions of thermal degradation of solids followingn-order kinetics. It has been demonstrated that, if heat and mass transfer effects are avoided, the reaction order obtained from this method will be equal to one whatever the reaction mechanism.     

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.     

Kissinger kinetic analysis of data obtained under different heating schedules

The dynamic heating rate method developed by TA Instruments (Hi-Res^TM) is a kind of sample controlled thermal analysis in which a linear relationship between the logarithm of the heating rate and the rate of mass change is imposed. It is shown in this paper that the reacted fraction at the maximum reaction rate strongly depends on the parameters selected for the Hi-Res heating algorithm, what invalidates the use of the Kissinger method for analysing Hi-Res data unless that the reaction fits a first order kinetic law. Only in this latter case, it has been demonstrated that it is not required that a constant value of the reacted fraction at the maximum reaction rate is fulfilled for determining the activation energy from the Kissinger method. In such a case the Kissinger plot gives the real activation energy, independently of both the heating schedule used and the value of the reacted fraction, α_m, at the maximum.     

Kinetics analysis of precipitation in a quasi-binary Cu-1 at.% CoTi alloy

The precipitation process for a concentration of CoTi of super-saturated solutions of Cu-0.50 at.% Co-0.45 at.% Ti (Cu-1 at.% CoTi) was studied through differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric curves between the environmental temperature and 900 K shows the presence of only one exothermic reaction attributed to the formation of CoTi particles in the matrix of copper. The energy of activation estimated by using the modified Kissinger method came out much lower than the corresponding to the diffusion of the cobalt and titanium in copper. We may attribute this fact to the strong contribution of the vacancies introduced by quenching. We used the formalism of Johnson-Mehl-Avrami (JMA) to assess the kinetic parameters. The energetic and kinetic evaluations and the molar heats of precipitation obtained from the isochor of van’t Hoff allow us to infer that the reaction corresponds to the formation of CoTi precipitates. The isothermal kinetics of precipitation reaction could be represented satisfactory by an overall kinetic function based in a macroscopic parameter (Vickers hardness). The kinetic parameters obtained from microhardness model are in agreements with those obtained from DSC traces.     

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.     

Stress concentration control in the problem of plane elasticity theory

In engineering practice, one of the important problems is the problem of finding full-strength contours which permits to control stress concentration at the hole boundary. The article addresses the mixed problem of plane elasticity theory for doubly-connected domain with partially unknown boundary conditions. In the presented work the stress state of the given body and full-strength contours were defined. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)