Showing papers by "Luc Pronzato published in 1995"

Modeling transient tracing in plug-flow reactors : a case study

Abstract: For heterogeneous catalysis, ordinary differential equations in time can be used to interpret transient tracer data obtained in a continuous stirred tank reactor or gradientless reactor in which a steady-state reaction is occurring. The same procedure is often used for plug-flow reactor modeling. However, for transient tracing data obtained with a plug-flow reactor operating under differential conversion, it is necessary to use a set of partial differential equations involving distance through the reactor as well as time. In this paper, the authors present a case study of methanation on a nickel catalyst to illustrate the modeling procedure needed to estimate the desired parameters.

Improving on Golden-Section Optimisation for Locally Symmetric Functions

Abstract: We consider the minimisation of a uniextremal function f(.) on [0,1] using a “second-order” algorithm. At each iteration the current feasible region is resealed to [0,1], so that the optimizing value x* in the initial [0,1]-interval varies from iteration to iteration, which defines a dynamic system. Many line-search algorithms exhibit chaotic behaviour when resealing is applied. If f(.)is symmetric around x*, the associated dynamic system is time-homogeneous and often possesses an invariant density. In a first part, we show that the asymptotic behaviour of the classical Golden-Section algorithm is the same for locally symmetric functions as for pure symmetric functions. We believe that this property is also true for other line-search algorithms, with sometimes a better ergodic rate than the Golden-Section algorithm. In a second part, we consider the case where the number of iterations is fixed a priori, with a dynamic-programming approach, using a uniform prior density on [0,1] for x*.