Densidad básica de la madera de Acacia melanoxylon R. Br en relación con la altura de muestreo, el árbol y el sitio

The aim of the work was to assess basic wood density variations of Acacia melanoxylon R.Br according to sample tree height, tree, and site. Twenty trees were selected from four sites in Buenos Aires Province, Argentine. Wood density was determined over two disc samples at four tree height (base, breast height, 30% and 50% of total tree height). According to determined ages, some trees were divided into two groups according to age (26-32 years and 9-12 years) and data were analyzed with an analysis of variance according to mixed model where tree was the random effecTrees represent 74 % of total random variance. Within tree, axial tendency of wood density was to decrease from the base toward breast height and then its value was stable to the top. This was consistent across all sites and age groups. Forest resource growing at Los Tuelches site presented the highest basic wood density.El objetivo del presente trabajo fue analizar las variaciones en la densidad básica de la madera de Acacia melanoxylon R.Br, según las alturas de muestreo en el fuste, los árboles y el sitio. Se seleccionaron 20 árboles en cuatro sitios de muestreo en la Provincia de Buenos Aires, Argentina. Se determinó la densidad de la madera sobre dos rodajas en cada una de cuatro alturas en el fuste (base, altura de pecho, 30% y 50% de la altura total). De acuerdo a la edad determinada, parte del material se reunió en dos grupos (26-32 años y 9-12 años) para los análisis de la varianza bajo modelos mixtos donde el árbol fue considerado como aleatorio. Asimismo, el árbol fue responsable del 74 % de la variación aleatoria total. Dentro del fuste se describió un descenso significativo de la densidad entre la base y la altura del pecho, región a partir de la cual la densidad mantuvo su valor hacia el extremo superior del fuste. Esta tendencia se manifestó en todos los sitios y agrupamientos por edades. El recurso implantado en la estación serrana Los Tuelches presentó las mayores densidades de la madera

An algebraic solution of driven single band tight binding dynamics

The dynamics of the driven tight binding model for Wannier-Stark systems is formulated and solved using a dynamical algebra. This Lie algebraic approach is very convenient for evaluating matrix elements and expectation values. It is also shown that a dynamical invariant can be constructed. A classicalization of the tight binding model is discussed as well as some illustrating examples of Bloch oscillations and dynamical localization effects.Comment: 13 pages; revised version (changed title and sections 6,7, added references

Plywoods of northeast argentinian woods and soybean protein-based adhesives: Relationship between morphological aspects of veneers and shear strength values

Three-ply plywoods were produced using pine and Eucalyptus northeast Argentinian woods. A no-added formaldehyde biobased-adhesive was used for assembly, based on chemically modified soy protein concentrate. In this work we focused on the relationship between bonding quality parameters of the plywoods and the morphology of the glued line. Wood characteristics such as contact angle, roughness, density and moisture content were measured prior to plywood assembly. Bonding quality parameters (percentage of wood failure and shear strength) of the plywood were measured according to Argentinean standard IRAM 9562 and the results were evaluated with respect to microscopic observations of the glue joint. Eucalyptus wood was suitable for plywood interior condition applications, while pine barely exceeded the standards imposed by the norm

Efecto del sitio, el origen y el clon sobre el crecimiento y propiedades de la madera de Populus

The objective of this paper was to study site, hybrid cross and clone effects on total height, BHD [Breast height diameter], volume, wood basic density, fibre length and yield, of eleven poplars clones. 10-year-old hybrid poplar clones were sampled at two sites in Argentina (MD and EG). The material studied consisted of two poplar hybrid crosses Populus deltoides x P. deltoides and P. deltoides x P. nigra (P. x canadensis = P. x euramericana), as well as P. deltoides. Sites influenced significantly growth traits and wood density, hybrid influenced tree height, wood density and fibre length and clones influenced all variables. MD trees were 5% higher and 2% denser than EG trees, but EG trees were 7% greater in BDH and 11% more volume than the MD trees. P. deltoides and P. deltoides intra specific crosses were 4% higher and 4% denser than P. x canadensis trees. P. x canadensis fibre length was 3% higher than P. x deltoides. According to all properties, difference between site and hybrid were not very importanThe properties of the clones had different responses regardless of the hybrid crosses. 610-31 and 564-17 clones (P. x deltoides) and 568-1 and Triplo (P. x canadensis) clones were distinguished.El objetivo del trabajo fue estudiar el efecto del sitio, el híbrido y el clon, sobre la altura total, DAP [Diámetro a la altura del pecho], volumen, densidad de la madera, longitud de fibras y rendimiento, de 11 clones de álamos. Se muestrearon ensayos de 10 años en dos sitios de Argentina (MD y EG). Los clones provienen de cruzamientos de P. deltoides, de cruzamientos de P. deltoides x P.nigra (P. x canadensis = P. euramericana) y P.deltoides. El sitio influyó significativamente en el crecimiento y densidad, el híbrido en la altura, densidad y longitud de fibras y los clones en todas las variables. Los árboles del sitio MD resultaron 5% más altos y 2% más densos, pero los ejemplares de EG resultaron con mayor DAP (7%) y volumen (11%). Los híbridos de P. x deltoides resultaron 4% mas altos y 4% más densos que los P. x canadensis. En longitud de fibras los híbridos P. x canadensis fueron 3% superiores. Las diferencias entre sitios y entre híbridos no resultaron tan marcadas considerando el conjunto de las propiedades. Los clones tuvieron diferente respuesta en las propiedades independientemente del cruzamiento del que derivan. Se destacaron los clones 610-31 y 564-17 (P. x deltoides) y 568-1 y Triplo (P. x canadensis)

Efecto del sitio, clon y edad sobre el crecimiento y la calidad de madera en sauces de corta rotación

The aim of the work was to asses the effects of site, clone and age on current annual increment, fibre length and wood density of 5 willow clones (S. babylonica var sacramenta «american»; hybrids of S. babylonica x S. alba «A 250-33» y «A 131-25» y S. matsudana x S. alba «A 13-44» y «NZ 26992»). Sites chosen were: Delta Medio (DM) del Río Paraná, Entre Ríos and Continental (C) Buenos Aires, Argentina. 13 years old trees were sampled and measurements of total height, diameter, growth rings, fibre length, wood density taken at 3 positions (ages) in each sample. Basal areas of current annual increments and weighted length and density were calculated. It was found that clone × site × age interaction was significant. The annual increments were found to be dependent on the site, the clone and the age under analysis. Weighted fibre length and wood density were found to be good estimates of wood quality, so the maximum fibre and density value depends both on clone growth patterns, implantation site and age. For American willow and hybrid 26992 of DM, the production of wood quality attained a maximum at 7 years old.El objetivo del trabajo fue evaluar el efecto del sitio, clon y la edad, sobre el incremento corriente anual, longitud de fibras y densidad de la madera en 5 clones de sauces (S. babylonica var sacramenta «americano»; híbridos de S. babylonica x S. alba «A 250-33» y «A 131-25» y S. matsudana x S. alba «A 13-44» y «NZ 26992»). Los sitios fueron: Delta Medio (DM) del Río Paraná Entre Ríos y Continental (C) Buenos Aires, Argentina. Sobre árboles de 13 años, se midieron: altura total, diámetro, anillos de crecimiento, longitud de fibras y densidad en 3 edades. Se calcularon los incrementos corrientes anuales medios en área basal, y la longitud y densidad ponderadas por área. La interacción sitio × clon × edad resultó significativa. Los incrementos corrientes son diferentes, dependiendo del sitio y el clon, según la edad que se analice. Tomando como indicador de calidad de madera a la longitud de fibras y densidad ponderadas, los valores máximos de dichas variables dependen de los patrones de crecimiento de cada clon, del sitio de implantación y de la edad. Para el sauce americano y el híbrido 26992 del sitio DM la mayor cantidad de madera de calidad se obtiene a los 7 años

Decoherence, tunneling and noise-activation in a double-potential well at high and zero temperature

We study the effects of the environment on tunneling in an open system described by a static double-well potential. We describe the evolution of a quantum state localized in one of the minima of the potential at $t=0$, both in the limits of high and zero environment temperature. We show that the evolution of the system can be summarized in terms of three main physical phenomena, namely decoherence, quantum tunneling and noise-induced activation, and we obtain analytical estimates for the corresponding time-scales. These analytical predictions are confirmed by large-scale numerical simulations, providing a detailed picture of the main stages of the evolution and of the relevant dynamical processes.Comment: Version to appear in Phys. Rev. E. 15 pages, 12 figures (low quality due to upload size limitations). Good quality figures in a pdf file can be downloaded from http://www.df.uba.ar/users/lombardo/tunne

Quantum effects after decoherence in a quenched phase transition

We study a quantum mechanical toy model that mimics some features of a quenched phase transition. Both by virtue of a time-dependent Hamiltonian or by changing the temperature of the bath we are able to show that even after classicalization has been reached, the system may display quantum behaviour again. We explain this behaviour in terms of simple non-linear analysis and estimate relevant time scales that match the results of numerical simulations of the master-equation. This opens new possibilities both in the study of quantum effects in non-equilibrium phase transitions and in general time-dependent problems where quantum effects may be relevant even after decoherence has been completed.Comment: 7 pages, 7 figures, revtex, important revisions made. To be published in Phys. Rev.

Nonadiabatic geometric phase induced by a counterpart of the Stark shift

We analyse the geometric phase due to the Stark shift in a system composed of a bosonic field, driven by time-dependent linear amplification, interacting dispersively with a two-level (fermionic) system. We show that a geometric phase factor in the joint state of the system, which depends on the fermionic state (resulting form the Stark shift), is introduced by the amplification process. A clear geometrical interpretation of this phenomenon is provided. We also show how to measure this effect in an interferometric experiment and to generate geometric "Schrodinger cat"-like states. Finally, considering the currently available technology, we discuss a feasible scheme to control and measure such geometric phases in the context of cavity quantum electrodynamics

Decoherence from a Chaotic Environment: An Upside Down "Oscillator" as a Model

Chaotic evolutions exhibit exponential sensitivity to initial conditions. This suggests that even very small perturbations resulting from weak coupling of a quantum chaotic environment to the position of a system whose state is a non-local superposition will lead to rapid decoherence. However, it is also known that quantum counterparts of classically chaotic systems lose exponential sensitivity to initial conditions, so this expectation of enhanced decoherence is by no means obvious. We analyze decoherence due to a "toy" quantum environment that is analytically solvable, yet displays the crucial phenomenon of exponential sensitivity to perturbations. We show that such an environment, with a single degree of freedom, can be far more effective at destroying quantum coherence than a heat bath with infinitely many degrees of freedom. This also means that the standard "quantum Brownian motion" model for a decohering environment may not be as universally applicable as it once was conjectured to be.Comment: RevTeX, 29 pages, 5 EPS figures. Substantially rewritten analysis, improved figures, additional references, and errors fixed. Final version (to appear in PRA