135 research outputs found
Cross and magnetic helicity in the outer heliosphere from Voyager 2 observations
Plasma velocity and magnetic field measurements from the Voyager 2 mission
are used to study solar wind turbulence in the slow solar wind at two different
heliocentric distances, 5 and 29 astronomical units, sufficiently far apart to
provide information on the radial evolution of this turbulence. The magnetic
helicity and the cross-helicity, which express the correlation between the
plasma velocity and the magnetic field, are used to characterize the
turbulence. Wave number spectra are computed by means of the Taylor hypothesis
applied to time resolved single point Voyager 2 measurements. The overall
picture we get is complex and difficult to interpret. A substantial decrease of
the cross-helicity at smaller scales (over 1-3 hours of observation) with
increasing heliocentric distance is observed. At 5 AU the only peak in the
probability density of the normalized residual energy is negative, near -0.5.
At 29 AU the probability density becomes doubly peaked, with a negative peak at
-0.5 and a smaller peak at a positive values of about 0.7. A decrease of the
cross-helicity for increasing heliocentric distance is observed, together with
a reduction of the unbalance toward the magnetic energy of the energy of the
fluctuations. For the smaller scales, we found that at 29 AU the normalized
polarization is small and positive on average (about 0.1), it is instead zero
at 5 AU. For the larger scales, the polarization is low and positive at 5 AU
(average around 0.1) while it is negative (around - 0.15) at 29 AU.Comment: 14 pages 5 figures. Accepted for publication on European Journal of
Mechanics B/Fluids (5/8/2015
Turbulence in the solar wind: spectra from Voyager 2 data at 5 AU
Fluctuations in the flow velocity and magnetic fields are ubiquitous in the
Solar System. These fluctuations are turbulent, in the sense that they are
disordered and span a broad range of scales in both space and time. The study
of solar wind turbulence is motivated by a number of factors all keys to the
understanding of the Solar Wind origin and thermodynamics. The solar wind
spectral properties are far from uniformity and evolve with the increasing
distance from the sun. Most of the available spectra of solar wind turbulence
were computed at 1 astronomical unit, while accurate spectra on wide frequency
ranges at larger distances are still few. In this paper we consider solar wind
spectra derived from the data recorded by the Voyager 2 mission during 1979 at
about 5 AU from the sun. Voyager 2 data are an incomplete time series with a
voids/signal ratio that typically increases as the spacecraft moves away from
the sun (45% missing data in 1979), making the analysis challenging. In order
to estimate the uncertainty of the spectral slopes, different methods are
tested on synthetic turbulence signals with the same gap distribution as V2
data. Spectra of all variables show a power law scaling with exponents between
-2.1 and -1.1, depending on frequency subranges. Probability density functions
(PDFs) and correlations indicate that the flow has a significant intermittency.Comment: 14 pages, 7 figures. Discussion improved since the previous versio
Turbulence in the Heliosheath: spectral analysis from Voyager 1 and 2 data
The Voyager 2 spacecraft is traveling through the heliosheath, the outermost layer in heliosphere where the solar wind is slowed by the interstellar gas, while Voyager 1 has entered the local interstellar medium. The they are providing the fist in-situ measurement of plasma and magnetic fields in that regions. We focus on the differences between the energetic particle intensity variations seen by the Voyager 1 and 2 crafts that are crossing the sectored and the unipolar as well as the sectored heliosheath regions, respectively. We try to provide a spectral analysis of the full heliosheath, characterizing the plasma and magnetic field turbulence through the estimate of the spectral properties in the different frequency ranges. Signal reconstruction techniques are mandatory to reconstruct spectra due to extreme data sparsity (up to 97\%\ missings in high resolution data beyond 80 AU). We use three different methods: correlation computation coupled with the maximum likelihood reconstruction, compress sensing and a genetic algorithm to estimate the gap influence on reconstructed spectra. These methods have been previously validated on 1979 data and synthetic hydrodynamics fluid turbulent fields
Human Indoleamine 2,3-dioxygenase 1 (IDO1) Expressed in Plant Cells Induces Kynurenine Production.
Genetic engineering of plants has turned out to be an attractive approach to produce various secondary metabolites. Here, we attempted to produce kynurenine, a health-promoting metabolite, in plants of Nicotiana tabacum (tobacco) transformed by Agrobacterium tumefaciens with the gene, coding for human indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme responsible for the kynurenine production because of tryptophan degradation. The presence of IDO1 gene in transgenic plants was confirmed by PCR, but the protein failed to be detected. To confer higher stability to the heterologous human IDO1 protein and to provide a more sensitive method to detect the protein of interest, we cloned a gene construct coding for IDO1-GFP. Analysis of transiently transfected tobacco protoplasts demonstrated that the IDO1-GFP gene led to the expression of a detectable protein and to the production of kynurenine in the protoplast medium. Interestingly, the intracellular localisation of human IDO1 in plant cells is similar to that found in mammal cells, mainly in cytosol, but in early endosomes as well. To the best of our knowledge, this is the first report on the expression of human IDO1 enzyme capable of secreting kynurenines in plant cells
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