3,084 research outputs found
Balances de elementos en un agroecosistema de caña de azúcar: II. Balance de Fósforo
The paper considers the application of the studies of nutrient cycling on the determination of phosphorus requirements in sugarcane plantations. The work was performed in a 4.5 ha experimental plot located in the valley of Yaracuy river in central, Venezuela. The plot was planted with the varieties Puerto Rico (PR) 1028 and Venezuela (V) 58-4. The principal flows of phosphorus, as well the quantities of this element in the soil-plant components were measured throughout the growing cycle of the crop (second ratoon). The inputs through precipitation (wet and dry) were high, that was associated with the intense agricultural (prescribed burning of sugarcane plantation) and industrial activities occurring in the area. The annual balance for both varieties was negative (-17 and - 23.3 kg.ha-1 for V 58-4 and PR 1028, respectively). The negative budget is mainly due to the important amounts of P that are exported with the cane stems. The losses must be compensated though fertilisation, nonetheless, preliminary results indicated no response to P dressing, suggesting that in the studied mollisol the internal processes e.g. Po mineralization and P solubilization, efficiently operate generating important available P levels. It was also found that the burning of the sugar cane plantation plays an important role in the recycling of phosphorus, since 25-30% of the P requirements of the varieties are reincorporated into the soil from the ashes
Balances de elementos en un agroecosistema de caña de azúcar: I. Balance de nitrógeno
In a tropical mollisol cropped with sugar cane the annual nitrogen balance was quantified taken into account the main i) inputs, ii) outputs and iii) transference of the element (N-NO3 + N-NH4) in the plant and soil subsystems. Precipitation input corresponded to 26.3 kg N.h–1.yr-1 mainly as N-NH4. After the rain water passes the sugar cane canopy there was a retention of N in the N-NH4 form, whereas N-NO3 was leached from the canopy. Outputs through leaching reached 5.3 kg N. ha-1.yr–1 mainly as N-NO3. An important part of total soil N is fixed to the 2:1 type clay particles (montmorillonitic), abundant in the studied mollisol. It is hypothesised that this fixed N could act as a soil N reserve. Net mineralization of the organic-N reached a high value (343 kg N.ha-1.yr–1) in accordance with the intense nitrification process occurring in the soil as a consequence of the convenient C/N ratio and urea fertilisation. Major N losses in the agrosystem correspond to cropping export and removal of ashes after fire. Yearly 98% of N accumulated in the aerial biomass is lost through those ways. In general the annual nitrogen budget is driven off through input by fertilisation and output through stem cropping and N volatilisation by fire
Birth, death and diffusion of interacting particles
Individual-based models of chemical or biological dynamics usually consider
individual entities diffusing in space and performing a birth-death type
dynamics. In this work we study the properties of a model in this class where
the birth dynamics is mediated by the local, within a given distance, density
of particles. Groups of individuals are formed in the system and in this paper
we concentrate on the study of the properties of these clusters (lifetime,
size, and collective diffusion). In particular, in the limit of the interaction
distance approaching the system size, a unique cluster appears which helps to
understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A:
Condensed matte
El reto de la conciliación trabajo y familia ¿qué nos estamos jugando?
Las dificultades que tienen las personas para encontrar el equilibrio entre su familia y su
trabajo profesional son una marca de identidad de la realidad social española actual. En
el proceso de cambio social que se ha producido de una forma vertiginosa en el último
siglo, junto a los grandes avances que han hecho, sin duda, más fácil la vida a las
personas, la confrontación familia-trabajo que actualmente se vive en muchas familias
es una de las sombras que ha acompañado a estas transformaciones. Aunque la
conciliación sea un reto global en la Unión Europea, e incluso podemos extenderlo a
muchas otras regiones del mundo, las dificultades difieren mucho de unos países a
otros, y España, junto con el resto de países de arco Mediterráneo, vive una situación
especialmente complicada en el entorno europeo. Una muestra de esta preocupación se
aprecia al comprobar que 2014 fue designado como el año europeo para la
reconciliación de la vida laboral y familiar.
El objetivo de este trabajo es dibujar un marco de comprensión amplio que ayude a
entender la importancia del tema resaltando las implicaciones que tiene la no
conciliación pero también los grandes beneficios que resultan de encontrar el equilibrio
y la armonía entre la vida familiar y la laboral. El texto se articula en tres partes: i) las
razones que explican que la conciliación sea en la actualidad especialmente uno de los
grandes retos que tiene la sociedad; ii) las razones que hacen necesario que se articulen
estrategias para superar este reto y los agentes que tienen un papel protagonista a la hora
de potenciar y llevar a cabo estas estrategias; y iii) las estrategias o las respuestas ante
los problemas de conciliación
Spontaneous Symmetry Breakdown in non-relativistic Quantum Mechanics
The advantages and disadvantages of some pedagogical non-relativistic
quantum-mechanical models, used to illustrate spontaneous symmetry breakdown,
are discussed. A simple quantum-mechanical toy model (a spinor on the line,
subject to a magnetostatic interaction) is presented, that exhibits the
spontaneous breakdown of an internal symmetry.Comment: 19 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1111.1213. Equations (30) and (31) have been corrected. Other minor
correction
Crystallization and melting of bacteria colonies and Brownian Bugs
Motivated by the existence of remarkably ordered cluster arrays of bacteria
colonies growing in Petri dishes and related problems, we study the spontaneous
emergence of clustering and patterns in a simple nonequilibrium system: the
individual-based interacting Brownian bug model. We map this discrete model
into a continuous Langevin equation which is the starting point for our
extensive numerical analyses. For the two-dimensional case we report on the
spontaneous generation of localized clusters of activity as well as a
melting/freezing transition from a disordered or isotropic phase to an ordered
one characterized by hexagonal patterns. We study in detail the analogies and
differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young
theory of equilibrium melting, as well as with another competing theory. For
that, we study translational and orientational correlations and perform a
careful defect analysis. We find a non standard one-stage, defect-mediated,
transition whose nature is only partially elucidated.Comment: 13 Figures. 14 pages. Submitted to Phys. Rev.
- …