A. Córdoba

Corrosive effects from the deposition of gaseous pollutants on surfaces of cultural and artistic value inside museums

The objectives of the project were to assess the critical relationships between environmental factors and damage of the artifacts and other cultural property exposed inside museums, by studying: (a) the outdoor/indoor pollutant concentration and their transfer inside the museum; (b) the distribution and circulation of pollutants inside the museum influenced by various factors; (c) chemical interactions between pollutants in the gas phase leading to removal and/or formation of secondary pollutants; (d) the final deposition of the indoor pollutants on surfaces of artistic interest and the damage on them, governed by strictly defined physicochemical parameters. All the above information, together with the main factors influencing each stage, were obtained by applying the methodology developed and described in detail here. Measurements of rate constants of reactions in the gas phase, of physicochemical deposition parameters on artefacts, and the synergistic effects of pollutants on the deposition parameters, were conducted. Seven PC programmes for analysing the experimental data were written and used. The pollutants, the solid materials and the museums chosen in this programme are only examples needed to develop the necessary methodology. The numerical results obtained serve the purpose of exemplifying the procedures and not enriching the worlds bibliography with useless empirical information. Two commercially available protectives for marble were investigated from the point of view of their reactivity towards SO2 by using a diffusional technique. From measurements of SO2 concentration carried out on three types of marble, the deposition velocities have been calculated. Indoor monitoring of the church of San Luigi dei Francesi and of the Museo della Civiltá Romana in Rome has shown that indoor production of nitrous acid most likely results from heterogeneous reactions indoors, on the walls and the exposed surfaces.

A Hh-driven gene network controls specification, pattern and size of the Drosophila simple eyes

During development, extracellular signaling molecules interact with intracellular gene networks to control the specification, pattern and size of organs. One such signaling molecule is Hedgehog (Hh). Hh is known to act as a morphogen, instructing different fates depending on the distance to its source. However, how Hh, when signaling across a cell field, impacts organ-specific transcriptional networks is still poorly understood. Here, we investigate this issue during the development of the Drosophila ocellar complex. The development of this sensory structure, which is composed of three simple eyes (or ocelli) located at the vertices of a triangular patch of cuticle on the dorsal head, depends on Hh signaling and on the definition of three domains: two areas of eya and so expression – the prospective anterior and posterior ocelli – and the intervening interocellar domain. Our results highlight the role of the homeodomain transcription factor engrailed (en) both as a target and as a transcriptional repressor of hh signaling in the prospective interocellar region. Furthermore, we identify a requirement for the Notch pathway in the establishment of en maintenance in a Hh-independent manner. Therefore, hh signals transiently during the specification of the interocellar domain, with en being required here for hh signaling attenuation. Computational analysis further suggests that this network design confers robustness to signaling noise and constrains phenotypic variation. In summary, using genetics and modeling we have expanded the ocellar gene network to explain how the interaction between the Hh gradient and this gene network results in the generation of stable mutually exclusive gene expression domains. In addition, we discuss some general implications our model may have in some Hh-driven gene networks.

Periodical forcing for the control of chaos in a chemical reaction.

Control of the chaotic behavior of a chemical system can be achieved perturbing periodically some control parameters of the system. This procedure based on external forcing, which is based on the phenomenon of resonance, can change a chaotic behavior into a periodical one by means of the application of a sinusoidal perturbation. In this paper, the influence of a periodical modulation added to the parameter controlling the oxygen adsorption rate in a cellular automaton (CA) model studying CO oxidation is analyzed. This CA model considers the oxidation reaction of CO on a catalytic surface, taking into account the catalyst temperature variation in order to analyze the reaction time oscillatory behavior. Simulations of the CA model exhibit chaotic and quasiperiodical behaviors, and it can be shown that the periodical forcing strategy can suppress the chaotic dynamics by means of the stabilization of periodical solutions.

Kinetic model for desorption of paired adatoms

By employing an extension of the Glauber–Ising model, the kinetics of the desorption of paired adatoms from a linear chain is studied. Three competitive mechanisms for changing a state of the system are allowed, namely desorption from or readsorption onto the chain or migration of the adatoms from site to site on the chain. The transition probabilities depend on an external field, on the interaction between nearest neighbors, and on three proper rate constants characterizing desorption, readsorption, and migration processes. An infinite set of coupled kinetic equations is obtained from the master equation. In order to compute the adsorption degree ϑ and the fraction of adjacent adatom pairs η, a ’’closure’’ approximation is taken. The steady‐state solution is in agreement with the exact result of the equilibrium statistical mechanics. We find that relaxation far from equilibrium is, in general, not describable by a single exponential. The relaxation is slower when mobility does not exist than when adatoms...

Optimization of energy supply systems with simulated annealing: continuous and discrete descriptions

We have developed continuous and discrete implementations of an optimization method (simulated annealing) to search the best way to fulfill different energy demands using different sets of transformation and storage devices. The simplicity of continuous description allows to implement the algorithm in an easy way, but for the discrete one we had to determine priorities in the devices contributions and to use a suitable code. We can conclude that the efficiency of both methods are good, but the discrete method is quicker than the continuous one.

OPTIMIZATION OF ENERGY SUPPLY SYSTEMS: SIMULATED ANNEALING VERSUS GENETIC ALGORITHM

We have applied two methods (simulated annealing and genetic algorithms) to search the solution of a problem of optimization with constraints in order to determine the best way to fulfill different energy demands using a set of facilities of energy transformation and storage. We have introduced a computational efficiency factor that measures the efficiency of the optimization algorithm and, as a result, we can conclude that for short computation times, genetic algorithms are more efficient than simulated annealing when demand profiles are not very long, whereas the latter is more efficient than the former for long computation time or for big demand profiles.

Genetic algorithms to optimize energy supply systems

Abstract A genetic algorithm, including crossover and mutation, has been applied to optimize energy supply systems, considering several energy demand profiles. In the crossover a “quasi-compatibility” condition is introduced, so that the constraints of the system may be taken into account, although certain violations of them are allowed at the expense of a penalty that decreases the fitness of the resulting offsprings. The genetic algorithm applied requires less computation time and provides better results than simulated annealing.

Far from equilibrium phase transitions in competitive adsorption: Dimension and closure approximation

Competitive adsorption of two species on a square lattice is considered, starting from a master equation. A doublet closure approximation is applied to obtain the kinetic equations; a Monte Carlo simulation is also performed. Unlike the results for a linear chain, multistability results, and thus there are far from equilibrium phase transitions. In this problem, the importance of the dimension of the system and the way the spatial correlations are treated in the approximation used is made clear.

Core regulatory network motif underlies the ocellar complex patterning in Drosophila melanogaster

Abstract During organogenesis, developmental programs governed by Gene Regulatory Networks (GRN) define the functionality, size and shape of the different constituents of living organisms. Robustness, thus, is an essential characteristic that GRNs need to fulfill in order to maintain viability and reproducibility in a species. In the present work we analyze the robustness of the patterning for the ocellar complex formation in Drosophila melanogaster fly. We have systematically pruned the GRN that drives the development of this visual system to obtain the minimum pathway able to satisfy this pattern. We found that the mechanism underlying the patterning obeys to the dynamics of a 3-nodes network motif with a double negative feedback loop fed by a morphogenetic gradient that triggers the inhibition in a French flag problem fashion. A Boolean modeling of the GRN confirms robustness in the patterning mechanism showing the same result for different network complexity levels. Interestingly, the network provides a steady state solution in the interocellar part of the patterning and an oscillatory regime in the ocelli. This theoretical result predicts that the ocellar pattern may underlie oscillatory dynamics in its genetic regulation.

A cellular automaton for a surface reaction: Stabilization from chaotic to periodical states

The chaotic behavior in a chemical reaction can be controlled by means of the method of external forcing. This technique, which is based on the resonance phenomenon, converts chaotic behavior into periodical one through application of a sinusoidal modulation. This paper analyzes the influence of a periodical perturbation on the environment temperature in a model of cellular automaton for the catalytic oxidation of CO. The model includes the variation of the catalyst temperature in order to analyze the oscillatory behavior of the reaction. The results of the simulations show chaotic and quasiperiodical behaviors. We point out that the periodical forcing can remove the chaotic dynamics through the stabilization of periodical solutions.