Modeling Regulation of Zinc Uptake via ZIP Transporters in Yeast and Plant Roots

In yeast (Saccharomyces cerevisiae) and plant roots (Arabidopsis thaliana) zinc enters the cells via influx transporters of the ZIP family. Since zinc is both essential for cell function and toxic at high concentrations, tight regulation is essential for cell viability. We provide new insight into the underlying mechanisms, starting from a general model based on ordinary differential equations and adapting it to the specific cases of yeast and plant root cells. In yeast, zinc is transported by the transporters ZRT1 and ZRT2, which are both regulated by the zinc-responsive transcription factor ZAP1. Using biological data, parameters were estimated and analyzed, confirming the different affinities of ZRT1 and ZRT2 reported in the literature. Furthermore, our model suggests that the positive feedback in ZAP1 production has a stabilizing function at high influx rates. In plant roots, various ZIP transporters are involved in zinc uptake. Their regulation is largely unknown, but bZIP transcription factors are thought to be involved. We set up three putative models: activator only, activator with dimerization and activator/inhibitor. These were fitted to measurements and analyzed. Simulations show that the activator/inhibitor model outperforms the other two in providing robust and stable homeostasis at reasonable parameter ranges.Comment: 23 pages including 2 tables and 7 figure

Homogenization approach to water transport in plant tissues with periodic microstructures

Water flow in plant tissues takes place in two different physical domains separated by semipermeable membranes: cell insides and cell walls. The assembly of all cell insides and cell walls are termed symplast and apoplast, respectively. Water transport is pressure driven in both, where osmosis plays an essential role in membrane crossing. In this paper, a microscopic model of water flow and transport of an osmotically active solute in a plant tissue is considered. The model is posed on the scale of a single cell and the tissue is assumed to be composed of periodically distributed cells. The flow in the symplast can be regarded as a viscous Stokes flow, while Darcy's law applies in the porous apoplast. Transmission conditions at the interface (semipermeable membrane) are obtained by balancing the mass fluxes through the interface and by describing the protein mediated transport as a surface reaction. Applying homogenization techniques, macroscopic equations for water and solute transport in a plant tissue are derived. The macroscopic problem is given by a Darcy law with a force term proportional to the difference in concentrations of the osmotically active solute in the symplast and apoplast; i.e. the flow is also driven by the local concentration difference and its direction can be different than the one prescribed by the pressure gradient.Comment: 31 page

Uso de las fichas didácticas en v grado de la educación primaria: visión de los educadores en San Ramón

Este artículo es parte de un proceso de investigación desarrollado en el año 2001 en dos circuitos escolares de la Dirección Regional de Educación de San Ramón. Presenta los resultados obtenidos de los educadores de V grado en relación con el uso de las fichas didácticas en Educación Primaria. La ficha didáctica es una técnica que se propone desde finales del siglo XIX, con el objetivo de individualizar la enseñanza y sigue manteniendo vigencia hasta el día de hoy. Por tal razón nos dimos a la tarea de investigar la concepción que manejan los educadores acerca de las fichas didácticas, las características, tipos, principios y valores que se pueden fortalecer, frecuencia con que se utilizan, razones de su uso, respuesta de los niños, ventajas, desventajas y sugerencias dadas por los educadores. Termina el artículo con algunas conclusiones en relación con la temática abordad

Water in massive star-forming regions: HIFI observations of W3 IRS5

We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-H_(2)^(17)O 1_(10)-1_(01), p-H_(2_^(18)O 1_(11)-0_(00), p-H_(2)O 2_(02)-1_(11), p-H_(2)O 1_(11)-0_(00), o-H_(2)O 2_(21)-2_(12), and o-H_(2)O 2_(12)-1_(01) lines, covering a frequency range from 552 up to 1669 GHz, have been detected at high spectral resolution with HIFI. The water lines in W3 IRS5 show well-defined high-velocity wings that indicate a clear contribution by outflows. Moreover, the systematically blue-shifted absorption in the H_(2)_O lines suggests expansion, presumably driven by the outflow. No infall signatures are detected. The p-H_(2)O 1_(11)-0_(00) and o-H_(2)O 2_(12)-1_(01) lines show absorption from the cold material (T ~ 10 K) in which the high-mass protostellar envelope is embedded. One-dimensional radiative transfer models are used to estimate water abundances and to further study the kinematics of the region. We show that the emission in the rare isotopologues comes directly from the inner parts of the envelope (T ≳ 100 K) where water ices in the dust mantles evaporate and the gas-phase abundance increases. The resulting jump in the water abundance (with a constant inner abundance of 10^(-4)) is needed to reproduce the o-H_(2)^(17)O 1_(10)-1_(01) and p-H_(2)^(18)O 1_(11)-0_(00) spectra in our models. We estimate water abundances of 10^(-8) to 10^(-9) in the outer parts of the envelope (T ≲ 100 K). The possibility of two protostellar objects contributing to the emission is discussed

Desarrollo de un sistema de alerta climática para acuicultura (parte i)

Desarrollo de un Sistema de Alerta Climática para Acuicultura (Parte I)A diferencia de la producción camaronera en el sudeste asiático, que se desarrolla en un escenario climático más estable, la acuicultura del camarón en Ecuador se ve influenciada por la estacionalidad anual, y por eventos correspondientes a una alta variabilidad climática en diferentes escalas de tiempo, tales como: El Niño/La Niña, correspondientes a la variabilidad interanual (Fig.1), y Eventos Climáticos de corto período que hacen presencia en nuestras costas con relativa frecuencia

Logic Negation with Spiking Neural P Systems

Nowadays, the success of neural networks as reasoning systems is doubtless. Nonetheless, one of the drawbacks of such reasoning systems is that they work as black-boxes and the acquired knowledge is not human readable. In this paper, we present a new step in order to close the gap between connectionist and logic based reasoning systems. We show that two of the most used inference rules for obtaining negative information in rule based reasoning systems, the so-called Closed World Assumption and Negation as Finite Failure can be characterized by means of spiking neural P systems, a formal model of the third generation of neural networks born in the framework of membrane computing.Comment: 25 pages, 1 figur

La matemática en la pintura costarricense: un primer acercamiento

El objetivo de la investigación consistió en determinar las formas en que la matemática puede influir en la pintura costarricense, lo cual permite contextualizar la matemática para su enseñanza y aportar en el desarrollo del conocimiento de esta disciplina. Las técnicas utilizadas para la investigación fueron, entrevista semiestructurada, entrevista a profundidad, análisis de textos. Los principales resultados detallan la necesidad de considerar previo a abordar la relación entre la matemática y la pintura costarricense, la presencia de elementos geométricos o aritméticos, elementos de diseño y composición, presencia de elementos geométricos y su impacto sensorial, y los efectos de la utilización de las tecnologías