Limonium vigoi (Plumbaginaceae), una nueva especie tetraploide del nordeste de la Península Ibérica

10 páginas, 5 figuras, 2 tablas.-- Parte sexta de la serie "A taxonomic and biosystematic revisión of the genus Limonium (Plumbaginaceae)".[EN] A new tetraploid agamic species, Limonium vigoi, is described from coastal populations of the Northeast of the Spain (Ebro delta). The new species is related, on morphological grounds, to L. girardianum (Guss.) Fourr. and L. grosii L. Llorens, from which it could be easily discriminated by its retuse leaves, the basal ones usually withered at anthesis, the very short (or even absent) leaf apiculum, the denser and longer (up to 0.7 mm) hairs of the calyx tube and the deeper colour of the corolla. In addition, L. girardianum is triploid, whereas L. vigoi and L. grosii are tetraploid. Limonium girardianum and L. grosii show the same pollen/stigma combination (A/cob type) which differs from that exhibited by L. vigoi (B/papillate type). The types of Limonium girardianum f. retusum Pignatti and L. glaucophyllum Pignatti, two taxa described from the Ebro delta, could not be distinguished from L. girardianum, but they clearly differed from L. vigoi.[ES] Se describe una nueva especie apomíctica (Limonium vigoi) procedente del nordeste de la Península Ibérica (delta del Ebro). Limonium vigoi presenta semejanzas morfológicas con L. girardianum (Guss.) Fourr. Y L. grosii L. Llorens, pero se diferencia de éstos por presentar hojas retusas, las básales normalmente marchitas en la antesis, mucrón terminal poco desarrollado o ausente, indumento calicinal constituido por tricomas más largos y color de la corola más oscuro. Además, L. girardianum es triploide, mientras que L. vigoi y L. grosii son tetraploides. Limonium girardianum y L. grosii presentan la misma combinación polínicoestigmática (A/cob), la cual difiere de la que posee L. vigoi (B/papilosa). El material tipo de Limonium girardianum i. retusum Pignatti y L. glaucophyllum Pignatti, dos táxones descritos del delta del Ebro, resulta indistinguible de L. girardianum y presenta claras diferencias respecto a L. vigoi.This work was supported by DGICYT research grant PB 93-0350.Peer reviewe

Field-Induced Transport in Sulfonated Poly(styrene-co-divinylbenzene) Membranes

Atomistic simulations have been carried to investigate electric field induced transport of hydronium ions in a sulfonated poly(styrene-co-divinylbenzene) membrane. In order to provide a good description of this cross-linked material, a methodology has been explicitly designed to construct a reliable model of the hydrated membrane. This model has been used to carry out molecular dynamics simulations in presence of electric fields, which varied from 0.001 to 3.0 V3 nm-1. Results show that the electric field affects the structure of the membrane producing both a redistribution of the unoccupied volume, which modifies the heterogeneity of the resin, and a rearrangement of the negatively charged sulfonate groups, which undergo a systematic alignment along the electric field direction. As was expected, the mobility of hydronium ions is enhanced with the strength of the electric field. Moreover, the electric field induces a significant rearrangement of the sulfonate groups, which is evidenced by the alignment of theC-S bonds along the direction of the field. The membrane has been found to behave as a spring, in which the force exerted by the electric field acts in opposite sense to the force exerted by the internal structure of the cross-linked material

A design study of high power microwave GaAs FET amplifier

SIGLEAvailable from British Library Document Supply Centre- DSC:D65244/86 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Field-Induced Transport in Sulfonated Poly(styrene-co-divinylbenzene) Membranes

Atomistic simulations have been carried to investigate electric field induced transport of hydronium ions in a sulfonated poly(styrene-co-divinylbenzene) membrane. In order to provide a good description of this cross-linked material, a methodology has been explicitly designed to construct a reliable model of the hydrated membrane. This model has been used to carry out molecular dynamics simulations in presence of electric fields, which varied from 0.001 to 3.0 V3 nm-1. Results show that the electric field affects the structure of the membrane producing both a redistribution of the unoccupied volume, which modifies the heterogeneity of the resin, and a rearrangement of the negatively charged sulfonate groups, which undergo a systematic alignment along the electric field direction. As was expected, the mobility of hydronium ions is enhanced with the strength of the electric field. Moreover, the electric field induces a significant rearrangement of the sulfonate groups, which is evidenced by the alignment of theC-S bonds along the direction of the field. The membrane has been found to behave as a spring, in which the force exerted by the electric field acts in opposite sense to the force exerted by the internal structure of the cross-linked material

Atomistic simulations of the structure of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) ion exchange resins

The microscopic structures of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) resins have been modeled by generating atomistic microstructures using stochastic-like algorithms, which are subsequently relaxed using molecular dynamics. Two different generation algorithms have been tested. The relaxation of the microstructures generated by the first algorithm, which is based on a homogeneous construction of the resin, leads to a significant overestimation of the experimental density as well as to an unsatisfactory description of the porosity. In contrast, the generation approach that combines algorithms for the heterogeneous growing and branching of the chains enables the formation of crosslinks with different topologies. In particular, the intrinsic heterogeneity observed in these resins is efficiently reproduced when the topological loops, which are defined by two or more crosslinks closing a cycle, are present in their microscopic description. Thus, the apparent density, porosity and pore volume estimated using microstructures with these topological loops, called super-crosslinks, are in very good agreement with the experimental results. Although the backbone dihedral angle distribution of the generated and relaxed models is not influenced by the topology, the number and type of crosslinks affect the medium- and long-range atomic disposition of the backbone atoms and the distribution of sulfonic groups. An analysis of the distribution of the local density indicates that super-crosslinks are responsible for the heterogeneous homogenization observed during the MD relaxation. Finally the pi-pi stacking interactions have been analyzed. Results indicate that those in which the two rings adopt a T-shaped disposition are considerably more abundant as compared to those with the co-facially oriented rings, independently of the resin topology.Peer Reviewe