Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects

Investigations of the magnetic properties of graphenes prepared by different methods reveal that dominant ferromagnetic interactions coexist along with antiferromagnetic interactions in all the samples. Thus, all the graphene samples exhibit room-temperature magnetic hysteresis. The magnetic properties depend on the number of layers and the sample area, small values of both favoring larger magnetization. Molecular charge-transfer affects the magnetic properties of graphene, interaction with a donor molecule such as tetrathiafulvalene having greater effect than an electron-withdrawing molecule such as tetracyanoethyleneComment: 16 pges, 5 figure

Quenching of fluorescence of aromatic molecules by graphene due to electron transfer

Investigations on the fluorescence quenching of graphene have been carried out with two organic donor molecules, pyrene butanaoic acid succinimidyl ester (PyBS, I) and oligo(p-phenylenevinylene) methyl ester (OPV-ester, II). Absorption and photoluminescence spectra of I and II recorded in mixture with increasing the concentrations of graphene showed no change in the former, but remarkable quenching of fluorescence. The property of graphene to quench fluorescence of these aromatic molecules is shown to be associated with photo-induced electron transfer, on the basis of fluorescence decay and time-resolved transient absorption spectroscopic measurements.Comment: 18 pages, 6 figure

Selección y obtención de material vegetal de vid tolerante a situaciones de estrés provocadas por falta de agua y exceso de sales en el medio

33 páginas.-- referencias.-- Proyecto para Tesis Doctoral.-- Memoria presentada en el XXXI Curso Internacional de Edafología y Biología VegetalDirector: Troncoso de Arce, AntonioEs de suma importancia para la economía de Chile, como país exportador de alimentos, mejorar la producción y calidad de sus prodllCtos agrícolas. Entre ellos destaca la producción de frutas y vinos, donde ocupa un lugar trascendental la uva. En efecto se debe indicar, que la producción de vino representa alrededor del 7% y la de uva de mesa un 8% del valor de la producción agropecuaria chilena. El 40% del total recaudado en este sector, se debe a la producción de vino, con 600 millones de litros producidos en 1982 logrados con una tasa de crecimiento anual de un 2% (Ortiz, 1983). El panorama cambia para la década de los 90 con una producción de sólo 43 millones de litros, a causa de la disposiciones reglamentarias establecidas, principalmente en la Comunidad Económica Europea, y el impuesto a nivel de productores aplicado en los Estados Unidos, sin embargo se evidencia indicios claros de una fuerte recuperación; el mayor interés por incrementar la superficie plantada y el aumento de las exportaciones, por ejemplo, ha incidido en un aumento de los precios internos. (Campos et al. 1991). En cuanto a la producción de uva para pisco (bebida alcohólica) las cifras indican una producción de 120 millones de kilos (Bulnes, 1988). El Norte de Chile representa la zona más extensa del país, y está clasificado como desierto absoluto, debido a sus condicionantes geomorfológicas y climáticas.Peer reviewe

Sistema Agrossilvipastoril na região sudoeste do Estado do Rio Grande do Sul.

bitstream/item/24472/1/Sistema-agrossilvipastoril-na-regiao-sudoeste-do-estado-do-Rio-Grande-do-Sul.pd

Evaluation of salt tolerance of in vitro-grown grapevine rootstock varieties

The response of 11 grapevine rootstock varieties to increasing salt concentrations (0, 50, 85, 120, 155 mM NaCl) was studied under in vitro and growth chamber conditions. The effect of salinity on the mortality of explants was compared with that of plantlets grown under growth chamber conditions and with data in literature on rootstock resistance under field conditions. In addition, in vitro stem elongation bud number, and rooting ability were related to salinity. The rootstock varieties can be divided into sensitive (41 B, R.Lot, 110 R, 140 R and 161-49), moderately tolerant (13.5 and Ramsey) and tolerant (196-17, CH-1, CH-2 and Superior). Measurements of the water and nutrient contents of plantlets indicate that increasing salt concentrations decreased the hydration of aerial parts and roots of all plants; however, the decrease of hydration was smaller in salt tolerant varieties. Increasing salt concentrations significantly reduced the K content and, to a smaller extent, the P and Ca contents. With and without salt treatments the levels of K and P were lower in sensitive plants. Na and Cl accumulated to a higher extent in tolerant plants. The tolerance to NaCl of in vitro-grown rootstocks seems to be due to their capacity to accumulate salt, to increase K concentration in the tissue and to maintain a high water content. Our results indicate that salt tolerance of grapevine varieties may be tested under growth chamber conditions and using in vitro explants

Influencia de la concentración de sacarosa en el medio, sobre la respuesta de material de vid "in vitro"

7 páginas, 8 figuras y 16 referencias.-- Trabajo presentado en el VI Simposium Nacional - II Ibérico sobre nutrición mineral de las plantas, Sevilla, del 12 al 15 de Noviembre de 1996.-- Entidades colaboradoras Junta de Andalucía, Universidad de Sevilla, Consejo Superior de Investigaciones Científicas, Sociedad Española de Fisiología Vegetal, El Monte, Caja de Huelva y Sevilla y Gat Fertilíquido. Editores científicos: Rafael Sarmiento Solís, Eduardo O. Leidi Montes y Antonio Troncoso de Arce.-- (Instituto de Recursos Naturales y Agrobiología de Sevilla).[EN]: The effects of two sucrose amounts, 20 and 30 gl(elevado a -1), added to the nutrient medium on the in vitro development of grapevine rootstocks 4 lB, 110 Richter, 196-17, 161-49 de Couderc and Rupestris de Lot, of Superior cultivar and of CH-I ,and CH-2 clones from Chile was studied. Medium with the lowest amount of sucrose favoured the aerial part growth of varieties ) 61-49, Rupestris de Lot, Superior and 196-17. This major growth of aerial part of explant (organs with clhorophyll), did not produce it in radical system. Development of this system was independent of sugar concentration in substrat and more in relation with grape variety Substrat with 20 gl(elevado a -1) of sucrose also shown a light major inclination to vitrification of in vitro plant. material[ES]: Se estudia el efecto de dos concentraciones (20 y 30 gl(elevado a -1)) de sacarosa en el medio de cultivo, sobre el desarrollo in vitro de los portainjertos de vid 41B, 110 de ichter,) 96-17, 161-49 de Couderc y Rupestris de Lot, del cultivar Superior y de los clones CH-) y CH-2 procedentes de Chile. El medio con la concentración mas baja de sacarosa favoreció, en general el crecimiento de la parte aérea del material de vid in vitro, en especial de las variedades 161-49, Rupestris de Lot, Superior y 196-17. Este mayor crecimiento de la parte aérea del explanto (órganos con clorofila), no se produjo en el sistema radical, cuyo desarrollo fue independiente de la concentración de azúcar en el medio y mas relacionable con la variedad de vid. El medio con 20 gl(elevado a -1) de sacarosa también mostró una ligera mayor predisposición a.la vitrificacón del material vegetal in vitro.Peer reviewe

Synthetic Aspects and Selected Properties of Graphene

Graphene has generated great sensation owing to its fascinating properties with possible potential applications. This two‐dimensional material exhibits half‐ integer quantum Hall effect and an ambipolar electric field effect, along with ballistic conduction of charge carriers. In this article, we provide a overview on some aspects of graphene devoting the special attention to synthesis, functionalization, self‐assembly, surface properties, gas adsorption and fluorescence quenching ability of graphene. Graphenes with varying number of layers can be synthesized by using different strategies. Graphene can be functionalized by different means in order to disperse it in various solvents. We also present the self‐assembly of graphene at the liquid‐liquid interface besides its surface properties including adsorption of hydrogen, carbon dioxide and methane. The remarkable property of graphene of quenching fluorescence of aromatic molecules is shown to be associated with photo‐induced electron transfe

Exponential localization of hydrogen-like atoms in relativistic quantum electrodynamics

We consider two different models of a hydrogenic atom in a quantized electromagnetic field that treat the electron relativistically. The first one is a no-pair model in the free picture, the second one is given by the semi-relativistic Pauli-Fierz Hamiltonian. We prove that the no-pair operator is semi-bounded below and that its spectral subspaces corresponding to energies below the ionization threshold are exponentially localized. Both results hold true, for arbitrary values of the fine-structure constant, $e^2$, and the ultra-violet cut-off, $\Lambda$, and for all nuclear charges less than the critical charge without radiation field, $Z_c=e^{-2}2/(2/\pi+\pi/2)$. We obtain similar results for the semi-relativistic Pauli-Fierz operator, again for all values of $e^2$ and $\Lambda$ and for nuclear charges less than $e^{-2}2/\pi$.Comment: 37 page