Multiscale velocity correlation in turbulence: experiments, numerical simulations, synthetic signals

Multiscale correlation functions in high Reynolds number experimental turbulence, numerical simulations and synthetic signals are investigated. Fusion Rules predictions as they arise from multiplicative, almost uncorrelated, random processes for the energy cascade are tested. Leading and sub-leading contribution, in the inertial range, can be explained as arising from a multiplicative random process for the energy transfer mechanisms. Two different predictions for correlations involving dissipative observable are also briefly discussed

The HIFI spectral survey of AFGL 2591 (CHESS). II. Summary of the survey

This paper presents the richness of submillimeter spectral features in the high-mass star forming region AFGL 2591. As part of the CHESS (Chemical Herschel Survey of Star Forming Regions) Key Programme, AFGL 2591 was observed by the Herschel/HIFI instrument. The spectral survey covered a frequency range from 480 up to 1240 GHz as well as single lines from 1267 to 1901 GHz (i.e. CO, HCl, NH3, OH and [CII]). Rotational and population diagram methods were used to calculate column densities, excitation temperatures and the emission extents of the observed molecules associated with AFGL 2591. The analysis was supplemented with several lines from ground-based JCMT spectra. From the HIFI spectral survey analysis a total of 32 species were identified (including isotopologues). In spite of the fact that lines are mostly quite week, 268 emission and 16 absorption lines were found (excluding blends). Molecular column densities range from 6e11 to 1e19 cm-2 and excitation temperatures range from 19 to 175 K. One can distinguish cold (e.g. HCN, H2S, NH3 with temperatures below 70 K) and warm species (e.g. CH3OH, SO2) in the protostellar envelope.Comment: Accepted to A&

Inhomogeneous turbulence in the vicinity of a large scale coherent vortex

We study the statistics of turbulent velocity fluctuations in the neighbourhood of a strong large scale vortex at very large Reynolds number. At each distance from the vortex core, we observe that the velocity spectrum has a power law ``inertial range'' of scales and that intermittency -- defined as the variation of the probability density function (PDF) of velocity increments as the length of the increment is varied -- is also present. We show that the spectrum scaling exponents and intermittency characteristics vary with the distance to the vortex. They are also influenced by the large scale dynamics of the vortex.Comment: submitted to europhys lett, 6 pages, 5 figure

A new scaling property of turbulent flows

We discuss a possible theoretical interpretation of the self scaling property of turbulent flows (Extended Self Similarity). Our interpretation predicts that, even in cases when ESS is not observed, a generalized self scaling, must be observed. This prediction is checked on a number of laboratory experiments and direct numerical simulations.Comment: Plain Latex, 1 figure available upon request to [email protected]

Double scaling and intermittency in shear dominated flows

The Refined Kolmogorov Similarity Hypothesis is a valuable tool for the description of intermittency in isotropic conditions. For flows in presence of a substantial mean shear, the nature of intermittency changes since the process of energy transfer is affected by the turbulent kinetic energy production associated with the Reynolds stresses. In these conditions a new form of refined similarity law has been found able to describe the increased level of intermittency which characterizes shear dominated flows. Ideally a length scale associated with the mean shear separates the two ranges, i.e. the classical Kolmogorov-like inertial range, below, and the shear dominated range, above. However, the data analyzed in previous papers correspond to conditions where the two scaling regimes can only be observed individually. In the present letter we give evidence of the coexistence of the two regimes and support the conjecture that the statistical properties of the dissipation field are practically insensible to the mean shear. This allows for a theoretical prediction of the scaling exponents of structure functions in the shear dominated range based on the known intermittency corrections for isotropic flows. The prediction is found to closely match the available numerical and experimental data.Comment: 7 pages, 3 figures, submitted to PR

Correlação do acúmulo de horas de frio entre duas estações agroclimatológicas situadas em diferentes posições geográficas no município de Pelotas-RS.

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Competitive ability of canola hybrids resistant and susceptible to herbicides.

ABSTRACT - This work aimed to compare the competitive ability of canola hybrids susceptible (conventional) or resistant to triazine or imidazolinone group herbicides, with turnip. The experiments were conducted in greenhouse, in a completely randomized design, with four replicates. The hybrids Hyola 571CL (resistant to imidazolinone), Hyola 555TT (resistant to triazine), and Hyola 61 (conventional) were used. The treatments consisted of ratios (100:0; 75:25; 50:50; 25:75; 0:100%) of canola and turnip plants. The evaluation was performed 44 days after emergence, determining the leaf área (AF), dry matter of aerial part (MSPA), and stature (EST) of the plants. The competitiveness analysis was performed through diagrams and interpretation of the competitiveness indexes. For the canola hybrids, the competition occurred by the same mean resources. There was damage to the crop growth in competition with the turnip. The turnip was not benefited only when in competition with Hyola 571CL hybrid, for the EST variable, and with the conventional canola, for the variable AF. There was significance for the competitiveness indexes, demonstrating that turnip is more competitive then the crop. Greater AF, MSPA, and EST occurred for canola plants in the smallest proportions of turnip and, for turnip plants, in the largest proportions of canola. The ability to compete with turnip is similar among hybrids, with injury to the crop and benefit to the weed, when competing. Interspecific competition is more damaging to canola hybrids; and intraspecific competition is more damaging to turnip. Keywords: Brassica napus L., Raphanus sativus L., interference, competitiveness. RESUMO - Este trabalho objetivou comparar a habilidade competitiva de híbridos de canola, suscetível (convencional) ou com resistência aos herbicidas do grupo das triazinas ou das imidazolinonas, com o nabo. Os experimentos foram conduzidos em casa de vegetação, no delineamento inteiramente casualizado com quatro repetições. Foram utilizados os híbridos Hyola 571CL (resistente a imidazolinonas), Hyola 555TT (resistente a triazinas) e Hyola 61 (convencional). Os tratamentos consistiram de proporções (100:0; 75:25; 50:50; 25:75; 0:100%) de plantas de canola e do nabo. A avaliação foi realizada aos 44 dias após a emergência, determinando-se a área foliar (AF), matéria seca de parte aérea (MSPA) e estatura (EST) de plantas. A análise da competitividade foi feita por meio de diagramas e interpretação dos índices de competitividade. Para os híbridos de canola, a competição ocorreu pelos mesmos recursos do meio. Houve prejuízo ao crescimento da cultura em competição com o nabo. O nabo somente não foi beneficiado quando em competição com o híbrido Hyola 571CL, para a variável EST, e com a canola convencional, para a variável AF. Houve significância para os índices de competitividade, demonstrando que o nabo é mais competitivo que a cultura. Maior AF, MSPA e EST ocorreu para plantas de canola nas menores proporções de nabo e, para plantas de nabo, nas maiores proporções de canola. A habilidade em competir com o nabo é semelhante entre os híbridos, havendo prejuízo à cultura e benefício à planta daninha, quando em competição. A competição interespecífica é mais prejudicial para os híbridos de canola, e a competição intraespecífica, para o nabo. Palavras-chave: Brassica napus L., Raphanus sativus L., interferência, competitividade

Experimental test of the Gallavotti-Cohen fluctuation theorem in turbulent flows

We test the fluctuation theorem from measurements in turbulent flows. We study the time fluctuations of the force acting on an obstacle, and we consider two experimental situations: the case of a von K\'arm\'an swirling flow between counter-rotating disks (VK) and the case of a wind tunnel jet. We first study the symmetries implied by the Gallavotti-Cohen fluctuation theorem (FT) on the probability density distributions of the force fluctuations; we then test the Sinai scaling. We observe that in both experiments the symmetries implied by the FT are well verified, whereas the Sinai scaling is established, as expected, only for long times