9,165 research outputs found
Subproton-scale cascades in solar wind turbulence: driven hybrid-kinetic simulations
A long-lasting debate in space plasma physics concerns the nature of
subproton-scale fluctuations in solar wind (SW) turbulence. Over the past
decade, a series of theoretical and observational studies were presented in
favor of either kinetic Alfv\'en wave (KAW) or whistler turbulence. Here, we
investigate numerically the nature of the subproton-scale turbulent cascade for
typical SW parameters by means of unprecedented high-resolution simulations of
forced hybrid-kinetic turbulence in two real-space and three velocity-space
dimensions. Our analysis suggests that small-scale turbulence in this model is
dominated by KAWs at and by magnetosonic/whistler fluctuations
at lower . The spectral properties of the turbulence appear to be in
good agreement with theoretical predictions. A tentative interpretation of this
result in terms of relative changes in the damping rates of the different waves
is also presented. Overall, the results raise interesting new questions about
the properties and variability of subproton-scale turbulence in the SW,
including its possible dependence on the plasma , and call for detailed
and extensive parametric explorations of driven kinetic turbulence in three
dimensions.Comment: 6 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
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
Collision-dependent power law scalings in 2D gyrokinetic turbulence
Nonlinear gyrokinetics provides a suitable framework to describe
short-wavelength turbulence in magnetized laboratory and astrophysical plasmas.
In the electrostatic limit, this system is known to exhibit a free energy
cascade towards small scales in (perpendicular) real and/or velocity space. The
dissipation of free energy is always due to collisions (no matter how weak the
collisionality), but may be spread out across a wide range of scales. Here, we
focus on freely-decaying 2D electrostatic turbulence on sub-ion-gyroradius
scales. An existing scaling theory for the turbulent cascade in the weakly
collisional limit is generalized to the moderately collisional regime. In this
context, non-universal power law scalings due to multiscale dissipation are
predicted, and this prediction is confirmed by means of direct numerical
simulations.Comment: 7 pages, 5 figures, accepted for publication in Physics of Plasma
Comparação entre metodologias para cálculo do Ãndice de manejo de carbono do solo em São LuÃs-MA.
O objetivo desse trabalho foi comparar o IMC calculado a partir de duas metodologias para determinação do teor de C lábil do solo (oxidação do C por K2Cr2O7 em diferentes nÃveis de acidez e fracionamento fÃsico da matéria orgânica do solo) em solos sob diferentes usos em São LuÃs-MA
Nitrous oxide emissions in agricultural soils: a review.
The greenhouse gases concentration in the atmosphere have significantly increased since the beginning of the Industrial Revolution. The most important greenhouse gases are CO2, CH4 and N2O, with CH4 and N2O presenting global warming potentials 25 and 298 times higher than CO2, respectively. Most of the N2O emissions take place in soils and are related with agricultural activities. So, this review article aimed at presenting the mechanisms of N2O formation and emission in agricultural soils, as well as gathering and discussing information on how soil management practices may be used to reduce such emissions. The N2O formation in the soil occurs mainly through nitrification and denitrification processes, which are influenced by soil moisture, temperature, oxygen concentration, amount of available organic carbon and nitrogen and soil C/N ratio. Among these factors, those related to soil could be easily altered by management practices. Therefore, understanding the processes of N2O formation in soils and the factors influencing these emissions is fundamental to develop efficient strategies to reduce N2O emissions in agricultural soils
Teores De C na biomassa microbiana do solo em diferentes usos da terra na periferia leste da Amazônia.
Emissões de N2O de um latossolo após a aplicação de fertilizantes nitrogenados.
O óxido nitroso (N2O) é o principal gás do efeito estufa emitido pelos solos agrÃcolas e sua emissão é influenciada pelo uso de fertilizantes nitrogenados. Este trabalho avaliou, sob condições controladas, o comportamento das emissões de N2O em amostras de um Latossolo Vermelho, em função da aplicação de duas fontes (nitrato de amônio e ureia) e de três doses (0,11 mg; 0,15 mg e 0,22 mg de N g-1 de solo) de nitrogênio. Os tratamentos foram aplicados na forma de solução, em delineamento inteiramente casualizado, com quatro repetições. Todos os tratamentos aumentaram as emissões de N2O em relação ao controle. O efeito da dose de N sobre as emissões de N2O foi mais pronunciado para a ureia. As emissões foram maiores e ocorreram mais rapidamente nos tratamentos com ureia do que naqueles com nitrato de amônio (maior emissão diária aos 9 e aos 12 dias, respectivamente). As emissões acumuladas ajustaram-se adequadamente a modelos logÃsticos em todos os tratamentos, indicando que estas curvas representam bem as emissões de N2O induzidas pela aplicação de fertilizantes nitrogenados sob condições controladas. Os resultados podem auxiliar no planejamento de pesquisas similares a serem conduzidas no campo
Leptospira fainei detected in testicles and epididymis of wild boar (Sus scrofa)
Leptospirosis is a re-emerging and worldwide diffused zoonosis. Recently, the high importance of their epidemiology was explained by the intermediate Leptospira strains. Among these strains, Leptospira fainei was the first intermediate strain detected in domestic and wild swine. Wild boars (Sus scrofa) are well known as a reservoir, as well as all swine, for pathogenic Leptospira, but very little information is available concerning intermediate Leptospira infection. The investigation aim was to evaluate if intermediate Leptospira can infect the reproductive systems of wild boars hunted in the Tuscany region (Italy), as previously demonstrated for pathogenic ones. The reproductive system tissue (testicles, epididymides, uteri), and placentas and fetuses, were collected from 200 regularly hunted animals. Bacteriological examination and real-time PCR were performed to detect intermediate Leptospira DNA. Unfortunately, no isolates were obtained. Using real-time PCR, in six (3%) male organs (both testicles and epididymis), intermediate Leptospira DNA was found. The amplification of the 16S rRNA gene identified that all DNA obtained belong to Leptospira fainei. The results of this investigation highlighted for the first time the localization of Leptospira fainei in the male wild boar reproductive system, opening up a new avenue to further investigate
Hydrogeology and hydrogeochemistry of an alkaline volcanic area: the NE Mt. Meru slope (East African Rift – Northern Tanzania)
Abstract. The objective of this study is to analyze the geochemical conditions associated with the presence of fluoride (F−) in the groundwater of an area of Northern Tanzania. The studied aquifers are composed of volcanic rocks such as phonolitic and nephelinitic lavas, basalts, lahars of various ages and mantling ash. Sedimentary rocks consisting of fine-grained alluvial and lacustrine deposits occur as well. Samples collected from springs, borehole and surface water, during two monitoring surveys, were analyzed for the various physico-chemical and isotopic parameters. The geochemical composition of water is typically sodium bicarbonate. High values of F− (up to 68 mg l−1) were recorded. The highest values of fluoride agreed with the highest values of pH, sodium and bicarbonate. Dissolution of major ions, exchange processes and precipitation of Ca2+ from super-saturated solutions joined with the local permeability and hydraulic gradients, control the fluoride mobilization and the contamination of the area
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