Papers by Francesc Giralt
AIChE Journal, 2004
A new approach is presented for the development of quantitative structure-property relations (QSP... more A new approach is presented for the development of quantitative structure-property relations (QSPR) based on the extraction of relevant molecular features with self-organizing maps and the use of a modified fuzzy-ARTMAP classifier for variable prediction. The present methodology is demonstrated for the development of a QSPR for the aqueous-phase infinite dilution activity coefficient ␥ ϱ , based on a data set of 325 diverse organic compounds. The QSPR was developed using a set of 11 molecular descriptors (four connectivities v 1-4 , Coulomb self-similarity measure, electron-nuclear attraction, dipole moment, sum of atomic numbers, number of filled levels, average polarizability, and nuclear-nuclear repulsion). The final set of molecular descriptors was selected from an initial pool of 23 topological and quantum chemical descriptors, including six molecular quantum similarity measures, by means of a topological analysis of self-organization of the data set. Additional interpolated information to enhance the training of the neural system was obtained from the self-organization analysis. The resulting fuzzy-ARTMAP-based QSPRs performed with errors that were on the average seven times smaller compared to previous published models. The use of only four molecular quantum similarity measures proved to be sufficient for building a ln␥ ϱ fuzzy-ARTMAP-based QSPR with reasonable accuracy.
Journal of Colloid and Interface Science, Mar 1, 2001
The potential effectiveness of poly(vinyl pyrrolidone) (PVP) as a zirconia surface modifier for p... more The potential effectiveness of poly(vinyl pyrrolidone) (PVP) as a zirconia surface modifier for protein adsorption reduction was investigated using lysozyme (LYS). The relatively small size of LYS (45 × 30 × 30Å) allowed for testing the adequacy of the graft polymerization method for producing a dense surface chain coverage to exclude LYS from direct interaction with the zirconia surface. The study demonstrated that a PVP brush layer is capable of reducing lysozyme adsorption. Overall, the maximum adsorption capacity decreased (by up to about 76%) due to surface modification with increasing polymer/silane surface coverage ratio (mol/mol). Adsorption reduction, due to protein exclusion from the surface by the tethered polymer layer, increased significantly when the distance between surface chains was less than the large axis of LYS (i.e., 45Å). The present results are encouraging and suggest further consideration of polymer-modified ceramic surfaces for reducing fouling of ceramic membranes during protein ultrafiltration and producing ceramic biocompatible surfaces for biomedical applications. C 2001 Academic Press
Int J Heat Mass Transfer, 1994
Commun Nonlinear Sci Numer Si, 2010
Fluid particle trajectories for the Rayleigh-Bénard problem in a cube with perfectly conducting l... more Fluid particle trajectories for the Rayleigh-Bénard problem in a cube with perfectly conducting lateral walls have been investigated. The velocity and temperature fields of the stationary flow solutions have been obtained by means of a parameter continuation procedure based on a Galerkin spectral method. The rich dynamics of the resulting fluid particle paths has been studied for three branches of stationary solutions and different values of the Rayleigh number within the range 1045 at a Prandtl number equal to 130. The stability properties and bifurcations of fixed points, which play a key role in the global dynamics, have been analyzed. Main periodic orbits and their stability character have also been determined. Poincaré maps reveal that regions of chaotic motion and regions of regular motion coexist inside the cavity. The boundaries of these three-dimensional regions have been determined. The metric entropy gives an indication of the mixing properties of the large chaotic zone.
The present theoretical-experimental study focuses on asymmetric flows undergoing rapid streamwis... more The present theoretical-experimental study focuses on asymmetric flows undergoing rapid streamwise evolution. To this end, the dynamic and thermal structure in a wake generated by a pair of cylinders which can be heated differentially is examined. Attention is given to the special case where the cylinders are of equal diameter. The different zones of the mean velocity and temperature fields as they undergo streamwise development are defined. In particular, the behavior in the near wake - the region of quasi-similitude - is considered.
Chemical use advanced automation systems that provide large amounts of accurate data information ... more Chemical use advanced automation systems that provide large amounts of accurate data information from the manufacturing process to plant engineers in real time.
The object of the study is the interaction of the wakes of two identical cylinders, the axes of w... more The object of the study is the interaction of the wakes of two identical cylinders, the axes of which are situated in the same plane normal to the stream and are at such a distance from each other that the initial coupling is weak. Beginning from a certain section, the mean dynamic field is equivalent to that of a single wake, and the similarity parameters of this wake are determined.
The Canadian Journal of Chemical Engineering
ABSTRACT
The transport equation for turbulent flows are deduced in tensorial notation and for a generalize... more The transport equation for turbulent flows are deduced in tensorial notation and for a generalized coordinate system. The equations of continuity, Navier-Stokes and Reynolds, as well as the transport equations for mean vorticity , turbulent kinetic energy and dissipation rate are presented.
The FORTRAN CFD code 3DINAMICS has been developed to simulate momentum, mass, and heat transfer i... more The FORTRAN CFD code 3DINAMICS has been developed to simulate momentum, mass, and heat transfer in laminar and turbulent unsteady three-dimensional flows. The code has been successfully applied to the simulation of several engineering flows, particularly we present four different ones: lid-driven cavity, natural convection in a cubical cavity, hydrodynamics in shallow ponds and three-dimensional transient flow in a dump combustor. Once this results have been obtained they have been interpreted converting the numerical files into pictures. In addition to the classical flow visualizations the current work explores two alternative magnitudes to describe the structural characteristics of flows. Figure 4. Stream lines for air at 8 m/s in the combustor
Information Processing Letters
We investigate the computational complexity of languages which have interactive proof systems of ... more We investigate the computational complexity of languages which have interactive proof systems of bounded message complexity. In particular, denoting the length of the input by n, we show that If L has an interactive proof in which the total communication is bounded by c(n) bits then L can be recognized by a probabilistic machine in time exponential in O(c(n) + log(n)). If L has a public-coin interactive proof in which the prover sends c(n) bits then L can be recognized by a probabilistic machine in time exponential in O(c(n) log(c(n)) + log(n)). If L has an interactive proof in which the prover sends c(n) bits then L can be recognized by a probabilistic machine with an NP-oracle in time exponential in O(c(n) log(c(n)) + log(n)).
Several models for the design and implementation of virtual sensor systems based on advanced neur... more Several models for the design and implementation of virtual sensor systems based on advanced neural architectures that are capable to infer on-line the properties of a manufactured product from real process variables were developed and tested. The architectures considered were a modified Fuzzy ARTMAP network, and two hybrid networks each combining a dynamic unsupervised classifier with a different kind of supervised predictor. A new method to construct dynamically the unsupervised layer was developed. The values of the melt index or quality of different LDPE grades produced in a tubular reactor were inferred at the beginning of the process cycle for different operation conditions and feed compositions. The most relevant process variables to build the sensor were selected using self-organizing maps and dissimilarity measures. All neural sensors outperformed predictors based on linear correlation techniques when appropriate information was provided for training. The results obtained indicate that the virtual sensors developed are capable of learning the relationships between process variables measured at the beginning of the production cycle and the quality parameters of the final product.
The traditional undergraduate engineeringcurriculum provides methods of analyzing and creatingpap... more The traditional undergraduate engineeringcurriculum provides methods of analyzing and creatingpaper designs, but does much less in teaching design formanufacture and production. The Capstone experience atthe University of Idaho uses a mentor-based ...
... JG Kawall, Francesc Xavier Grau Vidal, Jordi Gavaldà i Casado, JF Keffer, JA Ferré, Francesc ... more ... JG Kawall, Francesc Xavier Grau Vidal, Jordi Gavaldà i Casado, JF Keffer, JA Ferré, Francesc Giralt i Prat, Robert Manuel Gilabert Mallol. ATENCIÓ : Encara que actualment no es imprescindible per a accedir a aquest lloc, hi ha algunes pàgines que utilitzen Javascript, per ...
Two-component velocity signals, either u and v or u and w (hereinafter noted as u+v and u+w), sam... more Two-component velocity signals, either u and v or u and w (hereinafter noted as u+v and u+w), sampled in the far wake of a circular cylinder are analyzed using a pattern recognition technique. The results reported are ensemble averages of the instantaneous u+v or u+w velocity vectors, as well as of the uv product and of the envelope of the second derivatives of the velocities, the latter being used as a fine-scale activity detector. The organized motions observed are shear aligned double-roller eddies and eddies with vorticity parallel to the cylinder axis. Present results confirm that both kinds of organized eddies are not independent, but form a more complex coherent motion that can be described as a horseshoe or hairpin structure. The whole coherent activity of the instantaneous uv product is observed to be produced by the shear aligned vorticity of the double rollers. The fine-scale activity is also centered over the horseshoe, being more important toward the top of the structure where vorticity is parallel to the cylinder axis.
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Papers by Francesc Giralt