16 research outputs found
Nonlinear transverse cascade and two-dimensional magnetohydrodynamic subcritical turbulence in plane shear flows
We find and investigate via numerical simulations self-sustained
two-dimensional turbulence in a magnetohydrodynamic flow with a maximally
simple configuration: plane, noninflectional (with a constant shear of
velocity) and threaded by a parallel uniform background magnetic field. This
flow is spectrally stable, so the turbulence is subcritical by nature and hence
it can be energetically supported just by transient growth mechanism due to
shear flow nonnormality. This mechanism appears to be essentially anisotropic
in spectral (wavenumber) plane and operates mainly for spatial Fourier
harmonics with streamwise wavenumbers less than a ratio of flow shear to the
Alfv\'{e}n speed, (i.e., the Alfv\'{e}n frequency is lower than
the shear rate). We focused on the analysis of the character of nonlinear
processes and underlying self-sustaining scheme of the turbulence, i.e., on the
interplay between linear transient growth and nonlinear processes, in spectral
plane. Our study, being concerned with a new type of the energy-injecting
process for turbulence -- the transient growth, represents an alternative to
the main trends of MHD turbulence research. We find similarity of the nonlinear
dynamics to the related dynamics in hydrodynamic flows -- to the \emph{bypass}
concept of subcritical turbulence. The essence of the analyzed nonlinear MHD
processes appears to be a transverse redistribution of kinetic and magnetic
spectral energies in wavenumber plane [as occurs in the related hydrodynamic
flow, see Horton et al., Phys. Rev. E {\bf 81}, 066304 (2010)] and differs
fundamentally from the existing concepts of (anisotropic direct and inverse)
cascade processes in MHD shear flows.Comment: 19 pages, 7 figures, published in Phys. Rev. E 89, 043101 (2014
Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field
We investigate magnetohydrodynamic turbulence driven by the magnetorotational
instability (MRI) in Keplerian disks with a nonzero net azimuthal magnetic
field using shearing box simulations. As distinct from most previous studies,
we analyze turbulence dynamics in Fourier (-) space to understand its
sustenance. The linear growth of MRI with azimuthal field has a transient
character and is anisotropic in Fourier space, leading to anisotropy of
nonlinear processes in Fourier space. As a result, the main nonlinear process
appears to be a new type of angular redistribution of modes in Fourier space --
the \emph{nonlinear transverse cascade} -- rather than usual direct/inverse
cascade. We demonstrate that the turbulence is sustained by interplay of the
linear transient growth of MRI (which is the only energy supply for the
turbulence) and the transverse cascade. These two processes operate at large
length scales, comparable to box size and the corresponding small wavenumber
area, called \emph{vital area} in Fourier space is crucial for the sustenance,
while outside the vital area direct cascade dominates. The interplay of the
linear and nonlinear processes in Fourier space is generally too intertwined
for a vivid schematization. Nevertheless, we reveal the \emph{basic subcycle}
of the sustenance that clearly shows synergy of these processes in the
self-organization of the magnetized flow system. This synergy is quite robust
and persists for the considered different aspect ratios of the simulation
boxes. The spectral characteristics of the dynamical processes in these boxes
are qualitatively similar, indicating the universality of the sustenance
mechanism of the MRI-turbulence.Comment: 32 pages, 17 figures, accepted for publication in Ap
Active modes and dynamical balances in MRI-turbulence of Keplerian disks with a net vertical magnetic field
We studied dynamical balances in magnetorotational instability (MRI)
turbulence with a net vertical field in the shearing box model of disks.
Analyzing the turbulence dynamics in Fourier (-)space, we identified
three types of active modes that define turbulence characteristics. These modes
have lengths similar to the box size, i.e., lie in the small wavenumber region
in Fourier space labeled the vital area and are: (i) the channel mode - uniform
in the disk plane with the smallest vertical wavenumber,(ii) the zonal flow
mode - azimuthally and vertically uniform with the smallest radial wavenumber
and (iii) the rest modes. The rest modes comprise those harmonics in the vital
area whose energies reach more than of the maximum spectral energy. The
rest modes individually are not so significant compared to the channel and
zonal flow modes, however, the combined action of their multitude is dominant
over these two modes. These three mode types are governed by interplay of the
linear and nonlinear processes, leading to their interdependent dynamics. The
linear processes consist in disk flow nonmodality-modified classical MRI with a
net vertical field. The main nonlinear process is transfer of modes over
wavevector angles in Fourier space - the transverse cascade. The channel mode
exhibits episodic bursts supplied by linear MRI growth, while the nonlinear
processes mostly oppose this, draining the channel energy and redistributing it
to the rest modes. As for the zonal flow, it does not have a linear source and
is fed by nonlinear interactions of the rest modes.Comment: 28 pages, 16 figures, published in Ap
Sustaining turbulence in spectrally stable shear flows – interplay of linear transient growth and nonlinear transverse cascade
We analyze the sustaining mechanism of nonlinear perturbations/turbulence in spectrally stable smooth shear flows. The essence of the sustenance is a subtle interplay of linear transient growth of Fourier harmonics and nonlinear processes. In spectrally stable shear flows, the transient growth of perturbations is strongly anisotropic in spectral (k-)space. This, in turn, leads to anisotropy of nonlinear processes in k-space and, as a result, the main (new) nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that nonlinear state is sustained owing to the interplay of the linear nonmodal growth and the transverse cascade. The possibility of such course of events has been described in k-space by G. Chagelishvili, J.-P. Zahn, A. Tevzadze and J. Lominadze, A&A, 402, 401 (2003) that reliably exemplifies the well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. We present selected results of the simulations performed in different (HD and MHD; 2D and 3D; plane and Keplerian) shear flows to demonstrate the transverse cascade in action
Archaeomagnetic dating of Copper Age furnaces at Croce di Papa village and relations on Vesuvius and Phlegraean Fields volcanic activity
Metallurgic furnaces, discovered in the archaeological site of Croce di Papa, Nola, at 15 km NE from the Vesuvius summit, were dated here by using archaeomagnetic technique. They are positioned between the deposits of the Vesuvius eruption of Pomici di Avellino and of the Phlegraean eruption of Agnano-Monte Spina. A revision of available age data and associated uncertainties for these two eruptions was carried out in order to provide constraints on the Croce di Papa furnaces age determination. The adopted archaeomagnetic technique provides an accurate age of 3136–3027 BCE corresponding to 5085 to 4976 a BP that represents the upper age limit of the Agnano-Monte Spina eruption. This study provides evidences for the existence of human settlements in the Campanian Plain in the first century of the forth millennium BC and allow to assess the limited impact of the Agnano-Monte Spina eruption on climate and human settlement
Monitoring the environmental evolution and its relationship with anthropogenic activities using magnetic and geochemical proxies on Lake Melincué sediments
Two sediment cores, collected from the center of the Lake Melincué (Santa Fe, Argentina), were analyzed using rock magnetic results, element composition, Total Organic and Inorganic Carbon (TOC and TIC) and Total Nitrogen (TN) to reconstruct the environmental variations in the last three centuries, associated with climatic changes and/or human activities. 210Pb dating, chronostratigraphic markers, and paleomagnetic results were used to create the age model of the cores. Rock magnetic analyses suggest that (titano)magnetite and a low proportion of hematite are the main magnetic phases. In addition, geochemical results compared with rock magnetic analysis indicate the possible presence of diagenetic dissolution. Four well-differentiated environmental phases were found with variations from cold to more humid and warmer environmental conditions. Unit 0 from 1750 CE to 1783 CE with a cold environment and high lake level, Unit 1 from 1783 CE to 1878 CE with continuing cold environmental conditions but a low lake level, showing the end of the Little Ice Age (LIA) toward the top, Unit 2 from 1878 CE to 1874 CE with a wetter environment and Unit 3 from 1974 CE to 2016 CE with wet and warm conditions and a high lake level.Fil: Achaga, Romina Valeria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Gogorza, Claudia Susana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Irurzun, Maria Alicia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Gogichaishvili, Avtandil. Universidad Nacional Autónoma de México; MéxicoFil: Mestelán, S.. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Agronomía; ArgentinaFil: Ruiz Fernández, A. C.. Universidad Nacional Autónoma de México; MéxicoFil: Sánchez Cabeza, J. A.. Universidad Nacional Autónoma de México; MéxicoFil: Sánchez Bettucci, L.. Universidad de la República; UruguayFil: Sinito, Ana Maria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Morales, J.. Universidad Nacional Autónoma de México; MéxicoFil: Martínez, D.. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentin
The first meeting of the European Register of Cystic Echinococcosis (ERCE)
Cystic echinococcosis (CE) is a zoonotic parasitic disease endemic in southern and eastern European countries. The true prevalence of CE is difficult to estimate due to the high proportion of asymptomatic carriers who never seek medical attention and to the underreporting of diagnosed cases, factors which contribute to its neglected status. In an attempt to improve this situation, the European Register of Cystic Echinococcosis (ERCE), was launched in October 2014 in the context of the HERACLES project. ERCE is a prospective, observational, multicentre register of patients with probable or confirmed CE. The first ERCE meeting was held in November 2015 at the Italian National Institute of Health (Istituto Superiore di Sanita, ISS) in Rome, to bring together CE experts currently involved in the Register activities, to share and discuss experiences, and future developments.Although the Register is still in its infancy, data collected at the time of writing this report, had outnumbered the total of national cases reported by the European endemic countries and published by the European Centre for Disease Prevention and Control in 2015. This confirms the need for an improved reporting system of CE at the European level. The collection of standardized clinical data and samples is expected to support a more rational, stage-specific approach to clinical management, and to help public authorities harmonize reporting of CE. A better understanding of CE burden in Europe will encourage the planning and implementation of public health policies toward its control