| 1. |
- Tabiri, S, et al.
(author)
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- 2021
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swepub:Mat__t
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| 2. |
- Bravo, L, et al.
(author)
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- 2021
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swepub:Mat__t
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| 3. |
- Consolini, G., et al.
(author)
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A Hilbert-Huang transform approach to space plasma turbulence at kinetic scales
- 2017
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In: 16TH ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- Heliospheric space plasmas are highly turbulent media and display multiscale fluctuations over a wide range of scales from the magnetohydrodynamic domain down to the kinetic one. The study of turbulence features is traditionally based on spectral and canonical structure function analysis. Here, we present an novel approach to the analysis of the multiscale nature of plasma turbulent fluctuations by means of Hilbert-Huang Transform (HHT). In particular we present a preliminary application of this technique to magnetic field fluctuations at kinetic scales in a fast solar wind stream as observed by Cluster mission. The HHT-energy spectrum reveals the intermittent and multiscale nature of fluctuation frequency at kinetic scales indicating that there are no-persistent and long standing frequencies.
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| 4. |
- Consolini, G., et al.
(author)
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On the scaling features of magnetic field fluctuations at non-MHD scales in turbulent space plasmas
- 2016
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In: 15th Annual International Astrophysics Conference. - : IOP Publishing.
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Conference paper (peer-reviewed)abstract
- In several different contexts space plasmas display intermittent turbulence at magneto-hydro-dynamic (MHD) scales, which manifests in anomalous scaling features of the structure functions of the magnetic field increments. Moving to smaller scales, i.e. below the ion-cyclotron and/or ion inertial length, these scaling features are still observed, even though its is not clear if these scaling features are still anomalous or not. Here, we investigate the nature of scaling properties of magnetic field increments at non-MHD scales for a period of fast solar wind to investigate the occurrence or not of multifractal features and collapsing of probability distribution functions (PDFs) using the novel Rank-Ordered Multifractal Analysis (ROMA) method, which is more sensitive than the traditional structure function approach. We find a strong evidence for the occurrence of a near mono-scaling behavior, which suggests that the observed turbulent regime at non-MHD scales mainly displays a mono-fractal nature of magnetic field increments. The results are discussed in terms of a non-compact fractal structure of the dissipation field.
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| 5. |
- Dwivedi, N. K., et al.
(author)
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Implication of kinetic Alfvén waves to magnetic field turbulence spectra : Earth's magnetosheath
- 2019
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In: Astrophysics and Space Science. - : SPRINGER. - 0004-640X .- 1572-946X. ; 364:6
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Journal article (peer-reviewed)abstract
- In the present paper, we investigate the power-law behaviour of the magnetic field spectra in the Earth's magnetosheath region using Cluster spacecraft data under solar minimum condition. The power spectral density of the magnetic field data and spectral slopes at various frequencies are analysed. Propagation angle, kB, and compressibility, R vertical bar, are used to test the nature of turbulent fluctuations. The magnetic field spectra have the spectral slopes, , between -1.5 to 0 down to spatial scales of 20i (where i is ion gyroradius), and show clear evidence of a transition to steeper spectra for small scales with a second power-law, having between -2.6 to -1.8. At low frequencies, fsc<0.3fci (where fci is ion gyro-frequency), kB approximate to 90 degrees to the mean magnetic field, B0, and R vertical bar shows a broad distribution, 0.1R vertical bar 0.9. On the other hand at fsc>10fci, kB exhibits a broad range, 30 degrees kB90 degrees, while R vertical bar has a small variation: 0.2R vertical bar 0.5. We conjecture that at high frequencies, the perpendicularly propagating Alfven waves could partly explain the statistical analysis of spectra. To support our prediction of kinetic Alfven wave dominated spectral slope behaviour at high frequency, we also present a theoretical model and simulate the magnetic field turbulence spectra due to nonlinear evolution of kinetic Alfven waves. The present study also shows the analogy between the observational and simulated spectra.
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| 6. |
- Echim, M. M., et al.
(author)
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A Method to Estimate the Physical Properties of Magnetospheric Generators From Observations of Quiet Discrete Auroral Arcs
- 2019
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In: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 124:12, s. 10283-10293
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Journal article (peer-reviewed)abstract
- We discuss a method to estimate the properties of a magnetospheric generator using a quasi-electrostatic magnetosphere-ionosphere coupling model and in situ or remote sensing observations of discrete quiet arcs. We first construct an ensemble of Vlasov equilibrium solutions for generator structures formed at magnetospheric plasma interfaces. For each generator solution, we compute the ionospheric electric potential from the current continuity equation. Thus, we estimate the field-aligned potential drop that allows us to assess several properties of the discrete auroral arc, such as the field-aligned potential difference, the field-aligned current density, the flux of precipitating energy, and the height-integrated Pedersen conductance. A minimization procedure based on comparing the numerical results with observations is defined and applied to find which solution of the current continuity equation and which generator model give auroral arc properties that best fit the observations. The procedure is validated in a case study with observations by DMSP and Cluster and can be generalized to other types of data.
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| 7. |
- Flynn, Katherine M., et al.
(author)
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Profile of currently employed European food scientists and technologists : Education, experience and skills
- 2013
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In: International journal of food studies. - : ISEKI Food Association. - 2182-1054. ; 2:2, s. 137-149
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Journal article (peer-reviewed)abstract
- The food and drink (F & D) sector in Europe ranks low in innovation and the European F & D industry has been losing importance in the global market. The food professionals, i.e., food scientists and technologists (FSTs), may not be meeting the varied demands of the sector. Here, education, experience and skills of current FSTs were identified and compared geographic regions and employment areas. Between 2009 and 2012, 287 questionnaires representing over 4000 FSTs were collected from employers in 16 countries. Analyses showed that more than 80% of FSTs have a university degree; but only in Industry in the Central European region are most degrees in food science/technology. More than half of FSTs, and almost 60% in the South, have less than 10 years' experience. The most common FST job title is Quality Manager, but with several variations based on region and employment area. Among skills, the most common is Communicating; found in over 90% of FSTs in all regions and employment areas. Food Safety is the most common of the food sector-specific skills, present in more than 75% of FSTs, yet there are differences in food sector skills based on employment area. Overall, these data suggest similarities among currently employed food professionals throughout Europe; they are young and highly educated, but also differences, especially in their food sector-specific skills. An understanding of the current FST should contribute to the improvement of FST training and thus benefit the European food sector.
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| 8. |
- Lysak, R., et al.
(author)
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Quiet, Discrete Auroral Arcs : Acceleration Mechanisms
- 2020
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In: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 216:5
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Journal article (peer-reviewed)abstract
- The theory of the acceleration of auroral particles is reviewed, focusing on developments in the last 15 years. We discuss elementary plasma physics processes leading to acceleration of electrons to energies compatible with emission observed for quiet, discrete auroral arcs, defined as arcs that have time scales of minutes or more and spatial scales ranging from less than 1 km to tens of kilometers. For context, earlier observations are first described briefly. The theoretical fundamentals of auroral particle acceleration are based on the kinetic theory of plasmas, in particular the development of parallel electric fields. These parallel electric fields can either be distributed along the magnetic field lines, often associated with the mirror geometry of the geomagnetic field, or concentrated into narrow regions of charge separation known as double layers. Observations have indicated that the acceleration process depends on whether the field-aligned currents are directed away from the Earth, toward the Earth, or in mixed regions of currents often associated with the propagation of Alfvén waves. Recent observations from the NASA Fast Auroral SnapshoT (FAST) satellite, the ESA satellite constellation Cluster, and the Japanese Reimei satellite have provided new insights into the auroral acceleration process and have led to further refinements to the theory of auroral particle acceleration.
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| 9. |
- Voeroes, Zoltan, et al.
(author)
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Turbulence-Generated Proton-Scale Structures In The Terrestrial Magnetosheath
- 2016
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In: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 819:1
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Journal article (peer-reviewed)abstract
- Recent results of numerical magnetohydrodynamic simulations suggest that in collisionless space plasmas, turbulence can spontaneously generate thin current sheets. These coherent structures can partially explain the intermittency and the non-homogenous distribution of localized plasma heating in turbulence. In this Letter, Cluster multi-point observations are used to investigate the distribution of magnetic field discontinuities and the associated small-scale current sheets in the terrestrial magnetosheath downstream of a quasi-parallel bow shock. It is shown experimentally, for the first time, that the strongest turbulence-generated current sheets occupy the long tails of probability distribution functions associated with extremal values of magnetic field partial derivatives. During the analyzed one-hour time interval, about a hundred strong discontinuities, possibly proton-scale current sheets, were observed.
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