24 research outputs found
Acceleration of particles in imbalanced magnetohydrodynamic turbulence
The present work investigates the acceleration of test particles in balanced
and imbalanced Alfv\'{e}nic turbulence, relevant to the solar-wind problem.
These turbulent states, obtained numerically by prescribing the injection rates
for the ideal invariants, are evolved dynamically with the particles. While the
energy spectrum for balanced and imbalanced states is known, the impact made on
particle heating is a matter of debate, with different considerations giving
different results. By performing direct numerical simulations, resonant and
non-resonant particle accelerations are automatically considered and the
correct turbulent phases are taken into account. For imbalanced turbulence, it
is found that the acceleration rate of charged particles is reduced and the
heating rate diminished. This behaviour is independent of the particle
gyroradius, although particles that have a stronger adiabatic motion (smaller
gyroradius) tend to experience a larger heating.Comment: 5 pages 6 figure
Applications of large eddy simulation methods to gyrokinetic turbulence
The Large Eddy Simulation (LES) approach - solving numerically the large
scales of a turbulent system and accounting for the small-scale influence
through a model - is applied to nonlinear gyrokinetic systems that are driven
by a number of different microinstabilities. Comparisons between modeled, lower
resolution, and higher resolution simulations are performed for an experimental
measurable quantity, the electron density fluctuation spectrum. Moreover, the
validation and applicability of LES is demonstrated through a series of
diagnostics based on the free energetics of the system.Comment: 14 pages, 9 figure
Gyrokinetic turbulence:between idealized estimates and a detailed analysis of nonlinear energy transfers
Using large resolution numerical simulations of GK turbulence, spanning an
interval ranging from the end of the fluid scales to the electron gyroradius,
we study the energy transfers in the perpendicular direction for a
proton-electron plasma in a slab magnetic geometry. In addition, to aid our
understanding of the nonlinear cascade, we use an idealized test representation
for the energy transfers between two scales, mimicking the dynamics of
turbulence in an infinite inertial range. For GK turbulence, a detailed
analysis of nonlinear energy transfers that account for the separation of
energy exchanging scales is performed. We show that locality functions
associated with the energy cascade across dyadic (i.e. multiple of two)
separated scales achieve an asymptotic state, recovering clear values for the
locality exponents. We relate these exponents to the energy exchange between
two scales, diagnostics that are less computationally intensive than the
locality functions. It is the first time asymptotic locality is shown to exist
for GK turbulence and the contributions made by highly non-local interactions,
previously reported in the literature, are explained as very local transfers of
energy that occur between wavenumbers within the same dyadic signal. The
results presented here and their implications are discussed from the
perspective of previous findings reported in the literature and the idea of
universality of GK turbulence
Unpublished Mediterranean and Black Sea records of marine alien, cryptogenic, and neonative species
To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized
a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus,
Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020–2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes
textilis (Tunisia), and Botrylloides diegensis (Tunisia)