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  • Author or Editor: J. Domínguez x
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Abstract  

The Bercovici-Pata bijection maps the set of classical infinitely divisible distributions to the set of free infinitely divisible distributions. The purpose of this work is to study random matrix models for free infinitely divisible distributions under this bijection. First, we find a specific form of the polar decomposition for the Lévy measures of the random matrix models considered in Benaych-Georges [6] who introduced the models through their laws. Second, random matrix models for free infinitely divisible distributions are built consisting of infinitely divisible matrix stochastic integrals whenever their corresponding classical infinitely divisible distributions admit stochastic integral representations. These random matrix models are realizations of random matrices given by stochastic integrals with respect to matrix-valued Lévy processes. Examples of these random matrix models for several classes of free infinitely divisible distributions are given. In particular, it is shown that any free selfdecomposable infinitely divisible distribution has a random matrix model of Ornstein-Uhlenbeck type ∫0 e −1 dΨt d, d ≥ 1, where Ψt d is a d × d matrix-valued Lévy process satisfying an I log condition.

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Authors: J. Pérez, F. Rodríguez, M. Alonso, M. Oliet and J. Domínguez

Abstract  

The curing kinetics of lignin-novolac and methylolated lignin-novolac resins were studied using non-isothermal methods employing differential scanning calorimetry (DSC) at different heating rates. The Belichmeier, Ozawa and Kissinger methods were applied, which give the kinetic parameters of the curing process studied. In addition, the model-fitting Coats-Redfern method was used to analyze the experimental data. The kinetic study evaluated the effect of the lignin (softwood ammonium lignosulfonate), methylolated or not, on the resin curing process. Results for lignin-novolac and modified lignin-novolac resins were compared with a commercial novolac resin as a reference. When lignosulfonate is modified by methylolation and is incorporated in the novolac resin, there is an important reduction in activation energy. The lignin-novolac showed slightly higher values of activation energy than methylolated-lignin resins, but lower values than commercial resins. This behavior has been attributed to the extra methyol groups introduced by lignosulfonate.

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Abstract  

Both 9mTcO4 - and Rhodamine WT were employed as tracers to record the residence time distribution (RTD) in 5 segments located in the Almendares River in Havana City. Recovery calculations showed the conservative behavior of the 99mTcO4 - under the field conditions studied. The experimental residence time distribution curves from the second segment were convoluted for the d-Dirac injection at the beginning of the section. The spatial behavior of the conservative prompt spills throughout this river section was established for two extreme flow conditions.

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Authors: A. Farrona, M. Gallego, J. Vaquero and F. Domínguez-Castro

Exceptional geomagnetic storms were observed in late August and early September 1859. Auroras were observed around the world, and telegraph wires were damaged. Until now, there has been no evidence published of auroral observations in Spain during this famous space weather event. This paper presents Spanish observations that show the aspect of this great aurora from Spain, and the concurrent effects on European telegraph wires. We also computed the variation of the geomagnetic declination in Spain during recent centuries to put these records into context.

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Authors: J. Margalef-Roig, E. Outerelo-Domínguez and E. Padrón-Fernández
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Authors: L. Desdin, O. Dominguez, J. Moreno, L. Alfonso and M. Rodriguez

Abstract  

Determination of boric acid in high nickel content solutions during nickel cathode production was made by measuring the transmission loss of thermal neutrons. According to industrial requirements, adequate accuracy and reproducibility were obtained.

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Authors: J. Domínguez, A. Abreu, R. McCalla, J. Borroto, M. Ortueta and E. Pérez

Abstract  

The infusion rate of a slug of tracer into an anchor agitated 100-liter batch mixer was characterized by a decay rate constant. This constant was then used to define a dimensionless mixing-rate number which was related to the stirrer Reynolds number. This correlationship allows the calculation of time or rotational speed needed to achieve any desired degree of uniformity of the mixture.99mTc was used as radiotracer and the mixing process was followed by a scintillation Nal(Tl) counter situated on the reactor wall near the injection point.

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Authors: M. V. Alonso, M. Oliet, J. C. Domínguez, E. Rojo and F. Rodríguez

Abstract

Resol resins are used in many industrial applications as adhesives and coatings, but few studies have examined their thermal degradation. In this work, the thermal stability and thermal degradation kinetics of phenol–formaldehyde (PF) and lignin–phenol–formaldehyde (LPF) resol resins were studied using thermogravimetric analysis (TG) in air and nitrogen atmospheres in order to understand the steps of degradation and to improve their stabilities in industrial applications. The thermal stability of samples was estimated by measuring the degradation temperature (T d), which was calculated according to the maximum reaction rate criterion. In addition, the ash content was determined at 800 °C in order to compare the thermal stability of the resol resin samples. The results indicate that 30 wt% ammonium lignin sulfonate (lignin derivative) as filler in the formulation of LPF resin improves the thermal stability in comparison with PF commercial resin. The activation energies of degradation of two resol resins show a difference in dependence on mass loss, which allows these resins to be distinguished. In addition, the structural changes of both resins during thermal degradation were studied by Fourier transform infrared spectroscopy (FTIR), with the results indicating that PF resin collapses at 300 °C whereas the LPF resin collapses at 500 °C.

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