926 research outputs found
Plasma turbulence at ion scales: a comparison between PIC and Eulerian hybrid-kinetic approaches
Kinetic-range turbulence in magnetized plasmas and, in particular, in the
context of solar-wind turbulence has been extensively investigated over the
past decades via numerical simulations. Among others, one of the widely adopted
reduced plasma model is the so-called hybrid-kinetic model, where the ions are
fully kinetic and the electrons are treated as a neutralizing (inertial or
massless) fluid. Within the same model, different numerical methods and/or
approaches to turbulence development have been employed. In the present work,
we present a comparison between two-dimensional hybrid-kinetic simulations of
plasma turbulence obtained with two complementary approaches spanning about two
decades in wavenumber - from MHD inertial range to scales well below the ion
gyroradius - with a state-of-the-art accuracy. One approach employs hybrid
particle-in-cell (HPIC) simulations of freely-decaying Alfv\'enic turbulence,
whereas the other consists of Eulerian hybrid Vlasov-Maxwell (HVM) simulations
of turbulence continuously driven with partially-compressible large-scale
fluctuations. Despite the completely different initialization and
injection/drive at large scales, the same properties of turbulent fluctuations
at are observed. The system indeed self-consistently
"reprocesses" the turbulent fluctuations while they are cascading towards
smaller and smaller scales, in a way which actually depends on the plasma beta
parameter. Small-scale turbulence has been found to be mainly populated by
kinetic Alfv\'en wave (KAW) fluctuations for , whereas KAW
fluctuations are only sub-dominant for low-.Comment: 18 pages, 4 figures, accepted for publication in J. Plasma Phys.
(Collection: "The Vlasov equation: from space to laboratory plasma physics"
Biogenic amine producing capability of bacterial populations isolated during processing of different types of dry fermented sausages
Sunscreens’ uv filters risk for coastal marine environment biodiversity: A review
Considering the rapid growth of tourism in recent years and the acknowledgement that exposure to solar UV radiation may cause skin cancer, sunscreens have been widely used by beach-goers in recent decades. UV filters contained in sunscreens, however, were recently identified as emerging pollutants in coastal waters since they accumulate in the marine environment with different adverse effects. In fact, exposure to these components was proven to be toxic to most invertebrate and vertebrate marine species. Some UV filters are linked to the production of significant amounts of reactive oxygen species (ROS), such as hydrogen peroxide, and the release of inorganic micronutrients that may alter the status of coastal habitats. Bioaccumulation and biomagnification have not yet been fully addressed. This review highlights recent progress in research and provides a comprehensive overview of the toxicological and ecotoxicological effects of the most used UV filters both on the abiotic and biotic compartments in different types of coastal areas, to gain a better understanding of the impacts on coastal biodiversity
Questions to Ask Before You Join a Club
Despite the recent flurry of large transactions in which a consortium of private equity firms have teamed up to make joint bids and acquisitions, “club deals” themselves are not breaking news. In fact, they have been a staple of small- and middle-sized private equity M&A transactions for years. Recently, however, there has been a growing trend toward large club deals with enterprise values over $1 billion.1 Due to their size, complexity and, often, international dimension, these transactions have generated considerable attention in the business press and have prompted much discussion among private equity professionals and the limited partners whose money they manage
Scale dependence and cross-scale transfer of kinetic energy in compressible hydrodynamic turbulence at moderate Reynolds numbers
We investigate properties of the scale dependence and cross-scale transfer of
kinetic energy in compressible three-dimensional hydrodynamic turbulence, by
means of two direct numerical simulations of decaying turbulence with initial
Mach numbers M = 1/3 and M = 1, and with moderate Reynolds numbers, R_lambda ~
100. The turbulent dynamics is analyzed using compressible and incompressible
versions of the dynamic spectral transfer (ST) and the Karman-Howarth-Monin
(KHM) equations. We find that the nonlinear coupling leads to a flux of the
kinetic energy to small scales where it is dissipated; at the same time, the
reversible pressure-dilatation mechanism causes oscillatory exchanges between
the kinetic and internal energies with an average zero net energy transfer.
While the incompressible KHM and ST equations are not generally valid in the
simulations, their compressible counterparts are well satisfied and describe,
in a quantitatively similar way, the decay of the kinetic energy on large
scales, the cross-scale energy transfer/cascade, the pressure dilatation, and
the dissipation. There exists a simple relationship between the KHM and ST
results through the inverse proportionality between the wave vector k and the
spatial separation length l as k l ~ 3^1/2. For a given time the dissipation
and pressure-dilatation terms are strong on large scales in the KHM approach
whereas the ST terms become dominant on small scales; this is owing to the
complementary cumulative behavior of the two methods. The effect of pressure
dilatation is weak when averaged over a period of its oscillations and may lead
to a transfer of the kinetic energy from large to small scales without a net
exchange between the kinetic and internal energies. Our results suggest that
for large-enough systems there exists an inertial range for the kinetic energy
cascade ...Comment: 14 pages, 10 figure
Plasma turbulence and kinetic instabilities at ion scales in the expanding solar wind
The relationship between a decaying strong turbulence and kinetic instabilities in a slowly expanding plasma is investigated using two-dimensional (2D) hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and vanishing correlation between the two fields. A turbulent cascade rapidly develops; magnetic field fluctuations exhibit a power-law spectrum at large scales and a steeper spectrum at ion scales. The turbulent cascade leads to an overall anisotropic proton heating, protons are heated in the perpendicular direction, and, initially, also in the parallel direction. The imposed expansion leads to generation of a large parallel proton temperature anisotropy which is at later stages partly reduced by turbulence. The turbulent heating is not sufficient to overcome the expansion-driven perpendicular cooling and the system eventually drives the oblique firehose instability in a form of localized nonlinear wave packets which efficiently reduce the parallel temperature anisotropy. This work demonstrates that kinetic instabilities may coexist with strong plasma turbulence even in a constrained 2D regime
Questions to Ask Before You Join a Club
Despite the recent flurry of large transactions in which a consortium of private equity firms have teamed up to make joint bids and acquisitions, “club deals” themselves are not breaking news. In fact, they have been a staple of small- and middle-sized private equity M&A transactions for years. Recently, however, there has been a growing trend toward large club deals with enterprise values over $1 billion.1 Due to their size, complexity and, often, international dimension, these transactions have generated considerable attention in the business press and have prompted much discussion among private equity professionals and the limited partners whose money they manage
Three-dimensional local anisotropy of velocity fluctuations in the solar wind
We analyse velocity fluctuations in the solar wind at magneto-fluid scales in
two datasets, extracted from Wind data in the period 2005-2015, that are
characterised by strong or weak expansion. Expansion affects measurements of
anisotropy because it breaks axisymmetry around the mean magnetic field.
Indeed, the small-scale three-dimensional local anisotropy of magnetic
fluctuations ({\delta}B) as measured by structure functions (SF_B) is
consistent with tube-like structures for strong expansion. When passing to weak
expansion, structures become ribbon-like because of the flattening of SFB along
one of the two perpendicular directions. The power-law index that is consistent
with a spectral slope -5/3 for strong expansion now becomes closer to -3/2.
This index is also characteristic of velocity fluctuations in the solar wind.
We study velocity fluctuations ({\delta}V) to understand if the anisotropy of
their structure functions (SF_V ) also changes with the strength of expansion
and if the difference with the magnetic spectral index is washed out once
anisotropy is accounted for. We find that SF_V is generally flatter than SF_B.
When expansion passes from strong to weak, a further flattening of the
perpendicular SF_V occurs and the small-scale anisotropy switches from
tube-like to ribbon-like structures. These two types of anisotropy, common to
SF_V and SF_B, are associated to distinct large-scale variance anisotropies of
{\delta}B in the strong- and weak-expansion datasets. We conclude that SF_V
shows anisotropic three-dimensional scaling similar to SF_B, with however
systematic flatter scalings, reflecting the difference between global spectral
slopes.Comment: accepted in MNRA
Toward oscillations inhibition by mean-field feedback in Kuramoto oscillators
peer reviewedThis note shows that the oscillations in a network of all-to-all coupled Kuramoto oscillators can be inhibited by a scalar output feedback. More precisely, by injecting an input proportional to the oscillators mean-field, a set of isolated equilibria is shown to be almost globally attractive when natural frequencies are zero. The normal hyperbolicity of all relevant equilibria let us conjecture that this property persists in the presence of natural frequencies that are sufficiently small with respect to the coupling gain. This work constitutes a first step in the direction of testing the possible neuronal inhibition arising in deep brain stimulation treatment for neurological diseases. © 2011 IFAC
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