Dynamics and control of the expansion of finite-size plasmas produced in ultraintense laser-matter interactions

The strong influence of the electron dynamics provides the possibility of controlling the expansion of laser-produced plasmas by appropriately shaping the laser pulse. A simple irradiation scheme is proposed to tailor the explosion of large deuterium clusters, inducing the formation of shock structures, capable of driving nuclear fusion reactions. Such a scenario has been thoroughly investigated, resorting to two- and three-dimensional particle-in-cell simulations. Furthermore, the intricate dynamics of ions and electrons during the collisionless expansion of spherical nanoplasmas has been analyzed in detail using a self-consistent ergodic-kinetic model. This study clarifies the transition from hydrodynamic-like to Coulomb-explosion regimes

Long term dynamics of two populations of Prosopis caldenia Burkart

Los cambios más importantes registrados en la distribución del caldén (Prosopis caldenia Burkart) en la región semiárida central de Argentina, Incluyen el aumento de la densidad de esta especie y la invasión de pastizales naturales. Los factores causales y la dinámica de estos cambios no han sido detalladamente estudiados. En este trabajo se relaciona la dinámica de dos poblaciones de caldén con factores tales como manejo, fuego y precipitaciones. Se eligieron como áreas de estudios una planicie cuya vegetación original era un pastizal (sitio 1) y un bosque de caldén que originalmente fue una sabana (sitio 2). En cada sitio se determinaron los patrones espaciales en base a transectas y las tasas de Implantación las cuales fueron inferidas por dendroecologia. Las densidades estimadas fueron 586 y 1259 plantas/ha, para el sitio 1 y 2 respectivamente. No se encontraron evidencias de agrupamiento para la escala espacial de este estudio (p=0.52, sitio 1 y p=0.08, sitio 2 para n=112). Las edades de los individuos muestreados comprendieron un rango de 3 a 65 años en el sitio 1 y de 8 a 55 años en el sitio 2 (en este sitio 2 solo fueron muestreadas las plantas con diámetro menor de 30 cm). Primariamente los dos sitios fueron utilizados para erra de ovinos; durante ese periodo, las tasas de establecimiento fueron 0.99 plantas/ha/año (16 años) en el sitio 1, Y 10 plantas/ha/año (15 años) en el sitio 2. Posteriormente luego de diez años desde la introducción del ganado vacuno, las tasas ascendieron a 12.7 y 48.5 plantas/ha/año respectivamente. Un evento de fuego fue registrado en cada sitio (1980 en el sitio 1 y 1964 en el sitio 2) pero este factor no alteró la tendencia ascendente de la densidad. En el sitio 2 el Incendio fue contemporáneo con la introducción del ganado y coincide a su vez con un importante incremento en el establecimiento. No se encontró relación entre la dinámica de la población de caldén y las fluctuaciones en la precipitación anual o estacional. Las variaciones registradas en las tasas de establecimiento coincidieron con cambios en el manejo ganadero, confirmando la Importancia del ganado en la dispersión de las semillas de caldén.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la U.N.L.Pam.) Publicado en JOURNAL OF RANGE MANAGEMENT, 51 (6), November 199

Expansion of nanoplasmas and laser-driven nuclear fusion in single exploding clusters

The expansion of laser-irradiated clusters or nanodroplets depends strongly on the amount of energy delivered to the electrons and can be controlled by using appropriately shaped laser pulses. In this paper, a self-consistent kinetic model is used to analyze the transition from quasineutral, hydrodinamic-like expansion regimes to the Coulomb explosion (CE) regime when increasing the ratio between the thermal energy of the electrons and the electrostatic energy stored in the cluster. It is shown that a suitable double-pump irradiation scheme can produce hybrid expansion regimes, wherein a slow hydrodynamic expansion is followed by a fast CE, leading to ion overtaking and producing multiple ion flows expanding with different velocities. This can be exploited to obtain intracluster fusion reactions in both homonuclear deuterium clusters and heteronuclear deuterium-tritium clusters, as also proved by three-dimensional molecular-dynamics simulations.Comment: 9 pages, 3 figures, to appear in Plasma Physics and Controlled Fusio

Ecological Science Infrastructure for Sustainability Transformations in Rangelands

Sustainability transformations—deliberate and radical shifts in values, governance, and management regimes to achieve sustainability—are needed in rangelands as in other components of the Earth system. We review four concepts comprising an ecological science infrastructure to support such transformations. The foundation is standard measurement of rangeland conditions in the field, especially vegetation and soil properties that underpin the environmental aspects of sustainability. Big data resources, especially gridded spatial datasets produced by models and remote sensing, can be combined with field data and computational approaches to upscale information about rangeland conditions and produce additional indicators of ecosystem functions and services. State and transition models (STMs) linked to land types provide a means to interpret indicators and link interpretations to sustainable land management practices to manage change. Technologies for climate adaptation in rangelands also need to be linked to STM databases. Web and mobile technologies can put multifaceted science knowledge into the hands of pastoralists worldwide to support transformational changes in how rangelands are managed

Emergent global patterns of ecosystem structure and function from a mechanistic general ecosystem model

Anthropogenic activities are causing widespread degradation of ecosystems worldwide, threatening the ecosystem services upon which all human life depends. Improved understanding of this degradation is urgently needed to improve avoidance and mitigation measures. One tool to assist these efforts is predictive models of ecosystem structure and function that are mechanistic: based on fundamental ecological principles. Here we present the first mechanistic General Ecosystem Model (GEM) of ecosystem structure and function that is both global and applies in all terrestrial and marine environments. Functional forms and parameter values were derived from the theoretical and empirical literature where possible. Simulations of the fate of all organisms with body masses between 10 µg and 150,000 kg (a range of 14 orders of magnitude) across the globe led to emergent properties at individual (e.g., growth rate), community (e.g., biomass turnover rates), ecosystem (e.g., trophic pyramids), and macroecological scales (e.g., global patterns of trophic structure) that are in general agreement with current data and theory. These properties emerged from our encoding of the biology of, and interactions among, individual organisms without any direct constraints on the properties themselves. Our results indicate that ecologists have gathered sufficient information to begin to build realistic, global, and mechanistic models of ecosystems, capable of predicting a diverse range of ecosystem properties and their response to human pressures

What goes in does not always come out: The impact of the ruminant digestive system of sheep on plant material, and its importance for the interpretation of dung-derived archaeobotanical assemblages

On archaeological sites where livestock dung was a major fuel source, plant material that survives digestion intact may well be preserved in the remnants of dung-fuelled fires. Preserved plant remains which were derived from dung relate to the diet of animals, and thus provide a way of investigating the agro-pastoral economies of the past. In order to improve our understanding of the taphonomic processes to which plant material is exposed to during digestion, we applied archaeobotanical methods to the analysis of dung from sheep fed a known diet of cereal and wild plant material. Two clear patterns emerge from these investigations. First, cereal material (grain or chaff) survives digestion poorly and was rarely found in the dung analysed. Second, large proportions of seeds of various wild species survive digestion in an identifiable form, probably due to their small size and/or protective coating. These findings are crucial for reliable interpretation of dung-derived plant material in archaeological settings

Importance of predation and germination on losses from the seed bank of calden (Prosopis caldenia)

Caldén (Prosopis caldenia) seeds not dispersed by animals sometimes constitute a considerable number of seeds to the seed bank which may contribute to the species' dissemination. The monthly change in the number of viable non-animal dispersed seeds was evaluated over a one-year period. We determined the percentage germination of seeds and the amount of predation by bruchid beetles to learn how these factors influence seed longevity. Forty eight bags containing 10 fruits were placed in 4 sites below caldén tree canopies at the time of shedding (March). To monitor seed losses we randomly removed 1 bag per site every 25-35 days during a year. At the time of shedding, fruits contained 29 seeds, 73 +/- 5.0% which were viable and 9 +/- 2.2% attacked by bruchids. Viability decreased to 33 +/- 22.3% one year later. Loss of viability was described by a polynomial quadratic (y = 70.12 + 0.0238 t-0.0004 t2 (r2= 0.62)). Bags with germinated seeds were observed beginning in November. Percentage germinated seed increased 4.8 +/- 3.7% in the last month of sampling. Consumption of seeds by bruchids also increased in November, but the effect was highly variable. In the last month of sampling (March in the following year), 35 +/- 18.0% of seeds were affected by bruchids. A predictive seed longevity model was developed considering climatic variables, but data were well described only until January (y = 81.50-0.097 time-3.94 precipitation (r2= 0.66)). Undispersed seeds had a high rate of decay and low germination. Longevity was strongly affected by bruchid attack.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Long term dynamics of 2 populations of Prosopis caldenia Burkart

Invasion of pristine grasslands by caldén (Prosopis caldenia Burkart), and increased densities of this species in savannas are well-known vegetation changes in the semiarid region of central Argentina although little is known about its rates and patterns. In this paper we studied the relationship between dynamics of 2 representative P. caldenia populations and factors that could control the invasion process such as range management, fire events and precipitation regimes. Rates of implantation and spatial patterns are quantified using the present age distribution and dendroecological techniques. The pristine landscapes of the 2 study sites were grassland plains with (Site 2) and without trees (Site 1). The present density of the caldén is 586 and 1,259 shrubs/ha in Site 1 and 2, respectively. No evidence of clustering was found at the spatial scale of the study (p = 0.52, Site 1 and p = 0.08, Site 2 for n = 112). The ages of sampled individuals ranged from 3 to 65 years in site 1 and 8 to 55 years in Site 2 (only trees with diameter lower than 30 cm were sampled in Site 2). The importance of cattle as an effective disperser of caldén seeds was confirmed, as changes in measured establishment rates coincided fairly well with changes in cattle management. Establishment rates during the period of sheep grazing were 0.99 plant/ha/yr (16 years) in Site 1 and 10 plant/ha/yr (15 years) in Site 2. However, 10 years after the introduction of cattle these values reach 12.7 plant/ha/yr and 48.5 plant/ha/yr, respectively. One fire event occurred at each site (1980 in Site 1 and 1964 at Site 2). This factor did not change the density trend at Site 1, and at Site 2 it coincided with cattle introduction and caused an impressive increase in tree establishment. Fire was not an effective means of controlling P. caldenia populations. No relationship was found between population dynamics and available precipitation data.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202