8,004 research outputs found
Plasma turbulence at ion scales: a comparison between PIC and Eulerian hybrid-kinetic approaches
Kinetic-range turbulence in magnetized plasmas and, in particular, in the
context of solar-wind turbulence has been extensively investigated over the
past decades via numerical simulations. Among others, one of the widely adopted
reduced plasma model is the so-called hybrid-kinetic model, where the ions are
fully kinetic and the electrons are treated as a neutralizing (inertial or
massless) fluid. Within the same model, different numerical methods and/or
approaches to turbulence development have been employed. In the present work,
we present a comparison between two-dimensional hybrid-kinetic simulations of
plasma turbulence obtained with two complementary approaches spanning about two
decades in wavenumber - from MHD inertial range to scales well below the ion
gyroradius - with a state-of-the-art accuracy. One approach employs hybrid
particle-in-cell (HPIC) simulations of freely-decaying Alfv\'enic turbulence,
whereas the other consists of Eulerian hybrid Vlasov-Maxwell (HVM) simulations
of turbulence continuously driven with partially-compressible large-scale
fluctuations. Despite the completely different initialization and
injection/drive at large scales, the same properties of turbulent fluctuations
at are observed. The system indeed self-consistently
"reprocesses" the turbulent fluctuations while they are cascading towards
smaller and smaller scales, in a way which actually depends on the plasma beta
parameter. Small-scale turbulence has been found to be mainly populated by
kinetic Alfv\'en wave (KAW) fluctuations for , whereas KAW
fluctuations are only sub-dominant for low-.Comment: 18 pages, 4 figures, accepted for publication in J. Plasma Phys.
(Collection: "The Vlasov equation: from space to laboratory plasma physics"
Comparing persistence diagrams through complex vectors
The natural pseudo-distance of spaces endowed with filtering functions is
precious for shape classification and retrieval; its optimal estimate coming
from persistence diagrams is the bottleneck distance, which unfortunately
suffers from combinatorial explosion. A possible algebraic representation of
persistence diagrams is offered by complex polynomials; since far polynomials
represent far persistence diagrams, a fast comparison of the coefficient
vectors can reduce the size of the database to be classified by the bottleneck
distance. This article explores experimentally three transformations from
diagrams to polynomials and three distances between the complex vectors of
coefficients.Comment: 11 pages, 4 figures, 2 table
Efeito da profundidade de colocação do tubo de rega gota-a-gota na uniformidade de rega e na eficiência do uso da água em tomate de indústria
RESUMO
A influência da profundidade da colocação dos gotejadores na uniformidade de rega e na eficiência do uso da água foi avaliada, durante dois anos, num ensaio em “split-plot”, com quatro repetições, sendo o tratamento principal a profundidade de colocação do tubo de rega: à superfície do solo (P0), a 20 cm (PI) e a 40 cm (PII) e o secundário a cultivar: Brigade e H3044. Nos dois anos, o débito médio dos gotejadores foi semelhante nos diferentes tratamentos. Os coeficientes de uniformidade (CU) e de variação (CV) e a uniformidade de distribuição (UD), determinados após a colheita da cultura, não foram afectados pela profundidade de colocação do tubo, tendo variado respectivamente, entre 96,5 e 98,2%, 1,91 e 4,15% e 94,5 e 97,4%. A rega gota-a-gota subsuperficial, comparativamente com a superficial, contribuiu para o aumento da eficiência do uso da água (Produção comercial/ETa) em 14%, fundamentalmente devido a uma diminuição da ETa, na fase inicial da cultura
Nonlinear evolution of the magnetized Kelvin-Helmholtz instability: from fluid to kinetic modeling
The nonlinear evolution of collisionless plasmas is typically a multi-scale
process where the energy is injected at large, fluid scales and dissipated at
small, kinetic scales. Accurately modelling the global evolution requires to
take into account the main micro-scale physical processes of interest. This is
why comparison of different plasma models is today an imperative task aiming at
understanding cross-scale processes in plasmas. We report here the first
comparative study of the evolution of a magnetized shear flow, through a
variety of different plasma models by using magnetohydrodynamic, Hall-MHD,
two-fluid, hybrid kinetic and full kinetic codes. Kinetic relaxation effects
are discussed to emphasize the need for kinetic equilibriums to study the
dynamics of collisionless plasmas in non trivial configurations. Discrepancies
between models are studied both in the linear and in the nonlinear regime of
the magnetized Kelvin-Helmholtz instability, to highlight the effects of small
scale processes on the nonlinear evolution of collisionless plasmas. We
illustrate how the evolution of a magnetized shear flow depends on the relative
orientation of the fluid vorticity with respect to the magnetic field direction
during the linear evolution when kinetic effects are taken into account. Even
if we found that small scale processes differ between the different models, we
show that the feedback from small, kinetic scales to large, fluid scales is
negligable in the nonlinear regime. This study show that the kinetic modeling
validates the use of a fluid approach at large scales, which encourages the
development and use of fluid codes to study the nonlinear evolution of
magnetized fluid flows, even in the colisionless regime
Efeito do lodo de esgoto nos fluxos de gases na interface solo-atmosfera.
O objetivo do presente trabalho foi estudar o efeito da aplicação a longo prazo e continuada de lodo de esgoto da Estação de Tratamento de Esgoto de Barueri, SP, no fluxo de gases na interface soloatmosfera sob condições de campo e em condições tropicais.bitstream/CNPMA/5827/1/comunicado_32.pd
N2O emissions due to nitrogen fertilizer applications in two regions of sugarcane cultivation in Brazil.
Among the main greenhouse gases (CO2, CH4 and N2O), N2O has the highest global warming potential. N2O emission is mainly connected to agricultural activities, increasing as nitrogen concentrations increase in the soil with nitrogen fertilizer application. We evaluated N2O emissions due to application of increasing doses of ammonium nitrate and urea in two sugarcane fields in the mid-southern region of Brazil: Piracicaba (São Paulo state) and Goianésia (Goiás state). In Piracicaba, N2O emissions exponentially increased with increasing N doses and were similar for urea and ammonium nitrate up to a dose of 107.9 kg ha-1 of N. From there on, emissions nexponentially increased for ammonium nitrate, whereas for urea they stabilized. In Goianésia, N2O emissions nwere lower, although the behavior was similar to that at the Piracicaba site. Ammonium nitrate emissions increased linearly with N dose and urea emissions were adjusted to a quadratic equation with a maximum amount of 113.9 kg N ha-1. This first effort to measure fertilizer induced emissions in Brazilian sugarcane production not only helps to elucidate the behavior of N2O emissions promoted by different N sources frequently used in Brazilian sugarcane fields but also can be useful for future Brazilian ethanol carbon footprint studies
Draft Seagrass Bibliography Data Base
The following report describes in detail the elements of a literature search performed for the Southwest Florida Water Management District (SWFWMD), Department of Surface Water Improvement and Management (SWIM). The work was performed in accordance with the agreement between the District and Mote Marine Laboratory (MML), and comprises Task 3.0 (Literature Search) of the project entitled, Tampa Bay Water Quality Assessment- Determination of Environmental Requirements of Selected Populations
Persistent topology for natural data analysis - A survey
Natural data offer a hard challenge to data analysis. One set of tools is
being developed by several teams to face this difficult task: Persistent
topology. After a brief introduction to this theory, some applications to the
analysis and classification of cells, lesions, music pieces, gait, oil and gas
reservoirs, cyclones, galaxies, bones, brain connections, languages,
handwritten and gestured letters are shown
Graphic-based concept retrieval
Two ways of expressing concepts in the context of image retrieval are presented. One, Keypics, is on the side of an image owner, who wants the image itself to be found on the Web; the second, Trittico, is on the side of the image searcher. Both are based on the paradigm of human intermediation for overcoming the semantic gap. Both require tools capable of qualitative analysis, and have been experimented by using persistent homology
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