Graciela González

Viscosity Effects in Thin-Layer Electrodeposition

We present experimental results and a theoretical macroscopic model on the effects of viscosity in thin-layer electrochemical growth. The viscosity was changed through glycerol additions; simultaneous use was made of optical and schlieren techniques for tracking concentration and convective fronts, while pH indicators were used for migratory fronts. The theoretical model describes diffusive, migratory, and convective ion transport in a fluid subject to an electric field, The equations are written in terms of dimensionless quantities, in particular, the Migration, Peclet, Poisson, Reynolds, and electrical Grashof numbers, which are found to depend on viscosity, Experiments reveal that with increasing viscosity, convection decreases, concentration profiles are less pronounced, while electric resistance and voltage increase. Concentration and convective fronts slow down with viscosity, but their time scaling follows the Same law as for solutions without glycerol, only differing by a constant. Moreover, under constant electrical current, an increase in viscosity yields slower deposit front velocities, a more uniform deposit with smaller separation between branches, i.e., a change in morphology from more separated compact trees to a more dense, fractal-like structure.

Ion transport and deposit growth in spatially coupled bipolar electrochemistry

In spatially coupled bipolar electrochemistry, electrodissolution and electrodeposition processes in an applied electric field are exploited to create directional growth of copper deposits between two copper discs, not physically linked to an external voltage source. Here, we study the electric field in the whole cell through theoretical modeling, and ion transport in the interdisc region using optical and particle image velocimetry techniques. Their combined effect on incubation time and deposit morphology is assessed. Both the electric field and ion transport in the interdisc region are crucial factors in the characteristics of the interconnection. The model simulations reveal that the electric field is almost an order of magnitude larger in the region between discs as compared with the mean field value. Measurements and simulations show that the incubation time scales linearly with the inverse of the electric field, an indication that in this period, migration is the dominant transport mode. Experiments reveal that after branching develops, convection plays a relevant role as well, the contact growing linearly in time, with a change of the time/length slope at half the interdisc gap.

The genome organization and diversification of maize and its allied species revisited: evidences from classical and FISH-GISH cytogenetic analysis

The present review summarizes our classical and molecular cytogenetic investigations in the genus Zea. The results obtained from the meiotic behavior analysis of Zea species and hybrids, confirm the amphiploid nature of all species in the genus, with a basic number of x = 5 chromosomes. All species with 2n = 20 are diploidized allotetraploids, whereas Z. perennis (2n = 40) is an allooctoploid with four genomes somewhat divergent from one another. These analyses also revealed the existence of postzygotic reproductive isolation among Zea species. Our studies using genomic in situ hybridization (GISH) provide evidence about the evolutionary relationships among maize and its allied species, and reveal remarkable genomic divergences. Particularly, knob sequences were not completely shared between taxa previously considered to be closely related. Our data strongly suggest that the teosinte Z. mays parviglumis is not the only progenitor of cultivated maize. Introgression of Tripsacum into cultivated maize cannot be discarded.

Dynamical behaviour arising in the adaptive control of the generalized logistic map

Abstract Adaptive control schemes applied to the generalized logistic map are considered. The complex behaviour of the free system is removed and the dynamics of the resulting closed loop are completely described.

A polyelectrolyte-surfactant complex as support layer for membrane functionalization.

A polyelectrolyte-surfactant complex, polyallylamine-dodecylsulfate system, is presented as an alternative method for the modification of membranes. Due its chemical structure, the complex, once casted on a surface, is highly stable in aqueous solutions. This allows modifying with the same method different types of membranes, exemplified here by alumina and polycarbonate. Using different strategies, the complex system can also incorporate other elements useful for catalysis, biorecognition, or separation. Two applications are presented: the incorporation of gold nanoparticles to catalyze the reduction of 4-nitrophenol using a polycarbonate membrane, and the modification of alumina with a biotin derivative for the recognition of avidin in label-free sensors.

Use of AFLP and RAPD molecular genetic markers and cytogenetic analysis to explore relationships among taxa of the Patagonian Bromus setifolius complex

Bromus setifolius var. pictus (Hook) Skottsb., B. setifolius var. setifolius Presl. and B.setifolius var. brevifolius Ness are three native Patagonian taxa in the section Pnigma Dumort of the genus Bromus L. AFLP and RAPD analysis, in conjunction with genetic distance measurements and statistical techniques, revealed variation within this group and indicated that B. setifolius var. brevifolius was closely related to B. setifolius var. pictus, with both taxa being more distantly related to B. setifolius var. setifolius. Cytogenetic analysis confirmed the chromosomal number of B. setifolius var. pictus (2n = 70) and B. setifolius var. setifolius (2n = 28) and showed for the first time that B. setifolius var. brevifolius had 2n = 70. The combination of molecular genetic and cytogenetic evidence supported a species status for two of the three taxa and suggested hypotheses for the evolutionary origin of these complex taxa. Species status was also indicated for B. setifolius var. setifolius. Based on these findings, we suggest that B. setifolius var. pictus be referred to as B. pictus Hook var. pictus, and B. setifolius var brevifolius as B. pictus Hook var brevifolius. The correlation between AFLP diversity and variation in ecological parameters suggested that this marker system could be used to assess breeding progress and to monitor the domestication of Patagonian Bromus species for agronomic use.

Numerical Simulation of the Diffusion Processes in Nanoelectrode Arrays Using an Axial Neighbor Symmetry Approximation

Nanoelectrode arrays have introduced a complete new battery of devices with fascinating electrocatalytic, sensitivity, and selectivity properties. To understand and predict the electrochemical response of these arrays, a theoretical framework is needed. Cyclic voltammetry is a well-fitted experimental technique to understand the undergoing diffusion and kinetics processes. Previous works describing microelectrode arrays have exploited the interelectrode distance to simulate its behavior as the summation of individual electrodes. This approach becomes limited when the size of the electrodes decreases to the nanometer scale due to their strong radial effect with the consequent overlapping of the diffusional fields. In this work, we present a computational model able to simulate the electrochemical behavior of arrays working either as the summation of individual electrodes or being affected by the overlapping of the diffusional fields without previous considerations. Our computational model relays in dividing a regular electrode array in cells. In each of them, there is a central electrode surrounded by neighbor electrodes; these neighbor electrodes are transformed in a ring maintaining the same active electrode area than the summation of the closest neighbor electrodes. Using this axial neighbor symmetry approximation, the problem acquires a cylindrical symmetry, being applicable to any diffusion pattern. The model is validated against micro- and nanoelectrode arrays showing its ability to predict their behavior and therefore to be used as a designing tool.

A new adaptive scheme for a class of discrete-time nonlinear systems

Abstract A new adaptive control scheme for discrete-time systems is proposed. The objective is the tracking of the trajectory. Global boundedness convergence and boundedness are obtained for a certain subclass of nonlinear systems.

Adaptive control of linearizable discrete-time systems

Adaptive control is applied to a SISO discrete-time nonlinear system. The control objective is the tracking of the trajectory. A generalized classical adaptive scheme is proposed. Two results are obtained imposing different restrictions on the resulting closed-loop.

Nuevo recuento cromosómico para Blechnum hastatum (Blechnaceae-Pteridophyta), con un estudio de la ontogenia y tipos de leptoporangios adultos

Se da a conocer un nuevo recuento cromosomico para Blechnum hastatum y se presenta un analisis de la ontogenia del leptosporangio en ese taxon y en B. occidentale, asi como una comparacion con leptosporangios adultos de otras especies y subespecies del genero, como B. australe subsp. auriculatum, B. glandulosum y B. mochaenum subsp. mochaenum. En relacion con la citologia de B. hastatum, se contaron 33 bivalentes en diacinesis, lo que indica que se trata de un diploide con un numero cromosomico 2n=66, un dato que confrma un recuento previo y ubica al taxon en la secuencia de numeros cromosomicos basicos conocida para el genero, es decir x=33, que es el mas frecuente. En el estudio de la ontogenia de los esporangios se comprobo que se forman a partir de iniciales que se encuentran sobre la comisura y sobre la base del indusio; que desarrollan un pedicelo formado por celulas cortas en tres hileras en B. hastatum, la condicion aparentemente mas comun registrada para el genero, y celulas largas, tambien en tres hileras, en B. occidentale. Los pedicelos alcanzan su maximo desarrollo antes de que la capsula llegue a la etapa adulta. Los estomios tienen 6-8 celulas, las de la abertura engrosadas en forma de labio. Los anillos son verticales de hasta 14 celulas engrosadas en B. australe subsp. auriculatum y B. glandulosum, hasta 18 en B. hastatum y hasta 21 en B. mochaenum subsp. mochaenum y B. occidentale, llegan hasta la base misma de las capsulas y el numero de celulas engrosadas aparece como un caracter diagnostico nuevo en el genero.