Hydrolysis Rates of TMOS Catalyzed by Oxalic Acid and Stimulated by Ultrasound

A simple calorimetric method was employed to study the kinetics of the hydrolysis of the solventless TMOS-water mixtures, under ultrasound stimulation, as a function of the concentration of oxalic acid. The reaction rates were obtained, in relative units, from the measured thermal peak of the reaction as a non-separated function of both the sonication time and the instantaneous temperature of the medium. For concentrations of oxalic acid below 0.01 M, polycondensation reaction starts before complete hydrolysis. For concentrations of oxalic acid above 0.01 M, hydrolysis is complete and, in addition, the inverse of the time, as measured from the starting of ultrasound action until the maximum hydrolysis heat release, was found to be a reasonable relative measure of the average hydrolysis rate constant. The average hydrolysis rate constant was found to be proportional to the square root of the molar concentration of the oxalic acid. This result is in agreement with the literature if we assume small dissociation degree for the catalyst in such a solventless alkoxyde-water medium.     

Optimization of SO2 and NO x Emissions in Thermal Plants

This paper presents an environmental dispatch algorithm in a hydrothermal system and addresses the problem of minimization of emissions of SO₂ and NO _x caused by the operation of thermal plants. Several models have been used to represent the emissions function. In this paper, we first construct a quadratic model for both emissions: E(P)=α+β P+γ P ², where P is the power generated and the parameters were computed via the least-square criteria from several tests at thermal plants. We shall see that the problem consists in the minimization of a functional F(z) within the set of piecewise C ¹ functions that satisfy boundary conditions and non-holonomic inequality constraints. An optimal control technique is applied and Pontryagin’s theorem is employed. The algorithm proposed is easily implemented using the Mathematica Package and is applied to a sample system to illustrate the results obtained.     

Dual local completeness

The 1971 articles in which Saxon-Levin and Valdivia independently proved their Theorem feature two conditions equivalent to dual local completeness. One became Ruess' property (LC). The other is among new characterizations previously known only as necessary conditions.

     

Periodic perturbations of a class of resonant problems

We study the existence of solution for nonlinear problems at resonance under Dirichlet boundary conditions. We deal with PDE's as well as systems of ODE's. The nonlinear terms considered are periodic functions: in particular, the problem is strongly resonant at infinity. By means of variational methods, we prove nondegeneracy under some hypotheses on the nonlinearities. Received: 31 October 2003, Accepted: 12 July 2004, Published online: 8 February 2005 Mathematics Subject Classification (2000): 34B15, 35B34, 35J20 The authors have been supported by the Ministry of Science and Technology of Spain (BFM2002-02649), and by J. Andalucía (FQM 116)     

Surface Transitions of the Semi-Infinite Potts Model I: The High Bulk Temperature Regime

We propose a rigorous approach of Semi-Infinite lattice systems illustrated with the study of surface transitions of the semi-infinite Potts model.     

Array Modeling for MM-Wave Active Integrated Antennas

The design of active integrated antennas operating in the millimeter-wave (mm-wave) range requires a two-fold analysis: on one hand, the electromagnetic modeling of large planar arrays; on the other hand, the characterization of the active devices. In this paper we face the former task, by presenting an efficient method for the calculation of the voltages induced on all the elements of a planar array by the input (gaussian) beam, and the evaluation of the impedance matrix of the array. These parameters, together with the modeling of the active devices, allow for a full characterization of the active integrated antenna.     

Formation of a Kerr black hole from two stringy NUT objects

In this paper we show that an isolated Kerr black hole can be interpreted as arising from a pair of identical counter-rotating NUT objects placed on a symmetry axis at the appropriate critical distance from each other.