scholarly journals Spatiotemporal Analysis of Waves in Compressively Driven Magnetohydrodynamics Turbulence

2021 ◽  
Vol 922 (2) ◽  
pp. 240
Author(s):  
M. Brodiano ◽  
N. Andrés ◽  
P. Dmitruk
Keyword(s):  
Magnetic Field ◽  
Mach Number ◽  
Magnetic Energy ◽  
Normal Modes ◽  
Spatiotemporal Analysis ◽  
The Other ◽  
Three Dimensions ◽  
Direct Identification ◽  
Linear Waves ◽  
The Mean

Abstract Using direct numerical simulations (DNSs), the interaction between linear waves and turbulence under the compressible magnetohydrodynamic (CMHD) approach was studied. A set of DNSs in three dimensions for a spatial resolution of 1283 and 2563 were performed. A parametric study was carried out varying the sonic Mach number, the mean-magnetic field, and the compressibility amplitude of the forcing. Spatiotemporal spectra of the magnetic energy were built and analyzed, allowing for direct identification of all wave modes in a CMHD turbulent system and quantification of the amount of energy in each mode as a function of the wavenumber. Thus, linear waves were detected, that is Alfvén waves and fast and slow magnetosonic waves. Furthermore, different responses of the plasma were found according to whether the Mach number or the mean-magnetic field was varied. On the other hand, making use of spatiotemporal spectra and two different integration methods, we accurately quantified the amount of energy present in each of the normal modes. Finally, although the presence of linear waves was observed, in all the cases studied the system was mainly dominated by the nonlinear dynamics of the plasma.

Sex Differences in Privacy Preferences

1987 ◽  
Vol 64 (3_suppl) ◽  
pp. 1239-1242 ◽  
Author(s):  
Darhl M. Pedersen
Keyword(s):  
College Students ◽  
Sex Differences ◽  
The Other ◽  
Three Dimensions ◽  
Female College Students ◽  
Female College ◽  
Privacy Preferences ◽  
Other Hand ◽  
The Mean

A Privacy Questionnaire was administered to 118 male and 142 female college students to determine differences in the patterns of privacy preferences between the sexes. The questionnaire contained factor scales for measuring six independent types of privacy. t-tests showed that the means for women were significantly higher than those for men in their preferences for Intimacy with Family and Intimacy with Friends. On the other hand, for Isolation the mean for men was significantly higher than that for women. There were no significant differences between the means for the two sexes on the remaining three dimensions, Reserve, Solitude, and Anonymity.

On spiral coordinates with application to wave propagation

1995 ◽  
Vol 301 ◽  
pp. 153-173 ◽  
Author(s):  
L. M. B. C. Campos ◽  
P. J. S. Gil
Keyword(s):  
Magnetic Field ◽  
Wave Propagation ◽  
Magnetic Energy ◽  
Mass Density ◽  
Three Dimensions ◽  
Curvilinear Coordinates ◽  
Alfven Wave ◽  
Christoffel Symbols ◽  
Logarithmic Spirals ◽  
Arbitrary Frequency

We introduce a possibly new system of orthogonal curvilinear coordinates, whose coordinate curves are logarithmic spirals in the plane, supplemented by a cylindrical coordinate for three dimensions. It is shown that plane spiral coordinates form a oneparameter family, with equal scale factors along the two orthogonal coordinate curves, and constant Christoffel symbols. The equations of magnetohydrodynamics, which include those of fluid mechanics, are written in spiral coordinates and used to find a state of magnetohydrostatic equilibrium under a radial gravity field and spiral magnetic field, and to solve the equation of non-dissipative Alfvén waves in a spiral magnetic field in terms of Bessel functions. This exact solution specifies the evolution of wave perturbations (velocity and magnetic field) and energy variables (kinetic and magnetic energy densities and energy flux) with distance, for waves of arbitrary frequency. Both the frequency and the spiral angle are varied in plots of the waveforms, which show the effect on Alfvén wave propagation of three simultaneous effects: change in the mass density of the medium and in the strength and direction of the external magnetic field.

scholarly journals On heating of solar wind protons by the parametric decay of large-amplitude Alfvén waves

2018 ◽  
Vol 36 (6) ◽  
pp. 1647-1655 ◽  
Author(s):  
Horia Comişel ◽  
Yasuhiro Nariyuki ◽  
Yasuhito Narita ◽  
Uwe Motschmann
Keyword(s):  
Magnetic Field ◽  
Large Amplitude ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Alfven Wave ◽  
Sound Waves ◽  
Parametric Decay ◽  
Left Handed ◽  
Propagating Waves ◽  
The Mean

Abstract. By three-dimensional hybrid simulations, proton heating is investigated starting from a monochromatic large-amplitude Alfvén wave with left-handed circular polarization launched along the mean magnetic field in a low-beta plasma. We find that the perpendicular scattering is efficient in three dimensions and the protons are heated by the obliquely propagating waves. The thermal core proton population is heated in three dimensions as well in the longitudinal and parallel directions by the field-aligned and obliquely propagating sound waves out of the parametric decay. The astrophysical context is discussed.

scholarly journals The nature of mean-field generation in three classes of optimal dynamos

2020 ◽  
Vol 86 (1) ◽  
Author(s):  
Axel Brandenburg ◽  
Long Chen
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Boundary Conditions ◽  
Magnetic Energy ◽  
Mean Field ◽  
Dynamo Action ◽  
Magnetic Diffusivity ◽  
The Mean ◽  
The Magnetic Field ◽  
Mean Field Dynamo

In recent years, several optimal dynamos have been discovered. They minimize the magnetic energy dissipation or, equivalently, maximize the growth rate at a fixed magnetic Reynolds number. In the optimal dynamo of Willis (Phys. Rev. Lett., vol. 109, 2012, 251101), we find mean-field dynamo action for planar averages. One component of the magnetic field grows exponentially while the other decays in an oscillatory fashion near onset. This behaviour is different from that of an $\unicode[STIX]{x1D6FC}^{2}$ dynamo, where the two non-vanishing components of the planar averages are coupled and have the same growth rate. For the Willis dynamo, we find that the mean field is excited by a negative turbulent magnetic diffusivity, which has a non-uniform spatial profile near onset. The temporal oscillations in the decaying component are caused by the corresponding component of the diffusivity tensor being complex when the mean field is decaying and, in this way, time dependent. The growing mean field can be modelled by a negative magnetic diffusivity combined with a positive magnetic hyperdiffusivity. In two other classes of optimal dynamos of Chen et al. (J. Fluid Mech., vol. 783, 2015, pp. 23–45), we find, to some extent, similar mean-field dynamo actions. When the magnetic boundary conditions are mixed, the two components of the planar averaged field grow at different rates when the dynamo is 15 % supercritical. When the mean magnetic field satisfies homogeneous boundary conditions (where the magnetic field is tangential to the boundary), mean-field dynamo action is found for one-dimensional averages, but not for planar averages. Despite having different spatial profiles, both dynamos show negative turbulent magnetic diffusivities. Our finding suggests that negative turbulent magnetic diffusivities may support a broader class of dynamos than previously thought, including these three optimal dynamos.

scholarly journals Measuring stellar magnetic helicity density

2020 ◽  
Vol 493 (1) ◽  
pp. 1003-1012
Author(s):  
K Lund ◽  
M Jardine ◽  
L T Lehmann ◽  
D H Mackay ◽  
V See ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Magnetic Energy ◽  
Fundamental Property ◽  
Mass Range ◽  
Doppler Imaging ◽  
Magnetic Flux Density ◽  
Rossby Number ◽  
Solar Cycles ◽  
The Mean

ABSTRACT Helicity is a fundamental property of a magnetic field but to date it has only been possible to observe its evolution in one star – the Sun. In this paper, we provide a simple technique for mapping the large-scale helicity density across the surface of any star using only observable quantities: the poloidal and toroidal magnetic field components (which can be determined from Zeeman–Doppler imaging) and the stellar radius. We use a sample of 51 stars across a mass range of 0.1–1.34 M⊙ to show how the helicity density relates to stellar mass, Rossby number, magnetic energy, and age. We find that the large-scale helicity density increases with decreasing Rossby number Ro, peaking at Ro ≃ 0.1, with a saturation or decrease below that. For both fully and partially convective stars, we find that the mean absolute helicity density scales with the mean squared toroidal magnetic flux density according to the power law: $|\langle {h\, }\rangle |$ ∝ $\langle {\rm {{\it B}_{tor}}^2_{}\, \rangle }^{0.86\, \pm \, 0.04}$. The scatter in this relation is consistent with the variation across a solar cycle, which we compute using simulations and observations across solar cycles 23 and 24, respectively. We find a significant decrease in helicity density with age.

scholarly journals Cluster magnetic field observations in the magnetosheath: four-point measurements of mirror structures

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1421-1428 ◽  
Author(s):  
E. A. Lucek ◽  
M. W. Dunlop ◽  
T. S. Horbury ◽  
A. Balogh ◽  
P. Brown ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Flow Direction ◽  
Time Lag ◽  
Plasma Waves ◽  
Three Dimensions ◽  
Scale Size ◽  
Maximum Variance ◽  
First Results ◽  
The Mean ◽  
Statistical Survey

Abstract. The Cluster spacecraft have returned the first simultaneous four-point measurements of the magnetosheath. We present an analysis of data recorded on 10 November 2000, when the four spacecrafts observed an interval of strong mirrorlike activity. Correlation analysis between spacecraft pairs is used to examine the scale size of the mirror structures in three dimensions. Two examples are presented which suggest that the scale size of mirror structures is ~ 1500–3000 km along the flow direction, and shortest along the magnetopause normal (< 600 km), which, in this case, is approximately perpendicular to both the mean magnetic field and the magnetosheath flow vector. Variations on scales of ~ 750–1000 km are found along the maximum variance direction. The level of correlation in this direction, however, and the time lag observed, are found to be variable. These first results suggest that variations occur on scales of the order of the spacecraft separation ( ~ 1000 km) in at least two directions, but analysis of further examples and a statistical survey of structures observed with different magnetic field orientations and tetrahedral configurations will enable us to describe more fully the size and orientation of mirror structures.Key words. Magnetosphenic physics (magnetosheath; plasma waves and instabilities)

Mean induction and diffusion: the influence of spatial coherence

2009 ◽  
Vol 627 ◽  
pp. 403-421 ◽  
Author(s):  
ALICE COURVOISIER ◽  
DAVID W. HUGHES ◽  
STEVEN M. TOBIAS
Keyword(s):  
Magnetic Field ◽  
Spatial Coherence ◽  
Mean Diffusivity ◽  
Passive Scalar ◽  
The Other ◽  
Spatially Correlated ◽  
Molecular Diffusivity ◽  
Global Properties ◽  
The Mean ◽  
And Diffusion

Within the same framework we calculate the mean induction of a magnetic field and the mean diffusivity of a passive scalar, for two families of flows in which the degree of spatial decorrelation can be systematically adjusted. We investigate the dependence of these quantities both on the spatial decoherence and on the molecular diffusivity. We demonstrate that for flows with similar global properties, the mean induction is dramatically reduced as the flows become less spatially correlated; the mean diffusivity, on the other hand, shows no significant or systematic variation.

Bifurcations of magnetic topology by the creation or annihilation of null points

1996 ◽  
Vol 56 (3) ◽  
pp. 507-530 ◽  
Author(s):  
E. R. Priest ◽  
D. P. Lonie ◽  
V. S. Titov
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Comprehensive Treatment ◽  
Global Changes ◽  
Magnetic Topology ◽  
Cylindrically Symmetric ◽  
Saddle Node

Linear null points of a magnetic field may come together and coalesce at a secondorder null, or vice versa a second-order null may form and split, giving birth to a pair of linear nulls. Such local bifurcations lead to global changes of magnetic topology and in some cases release of magnetic energy. In two dimensions the null points are of X or O type and the flux function is a Hamiltonian; the magnetic field may undergo addle-centre, pitchfork or degenerate resonant bifurcations. In three dimensions the null points and their creation or annihilation by bifurcations are considerably more complex. The nulls possess a skeleton consisting of a spine curve and a fan surface and are of radial-type (proper or improper) or spiral-type; the type of null and the inclination of spine and fan depend on the magnitudes of the current components along and normal to the spine. In cylindrically symmetric fields a comprehensive treatment is given of the various types of saddle-node, Hopf and saddle-node—Hopfbifurcations. In fully three-dimensional situations examples are given of saddle-node and degenerate bifurcations, in which generically two nulls are created or destroyed and are joined by a separator field line, which is the intersection of the two fans. Furthermore, global bifurcations can create chaotic field lines that could perhaps trigger energy release in, for example, solar flares.

Waves on the beta-plane over sparse topography

2000 ◽  
Vol 423 ◽  
pp. 263-273 ◽  
Author(s):  
E. S. BENILOV
Keyword(s):  
Dispersion Relation ◽  
The Other ◽  
Coriolis Parameter ◽  
Main Assumption ◽  
Linear Waves ◽  
Beta Plane ◽  
The Mean ◽  
Wave Modes

This paper deals with linear waves on the beta-plane over topography. The main assumption is that the topography consists of isolated radially symmetric irregularities (random or periodic), such that their characteristic radii are much smaller than the distances between them. This approximation allows one to obtain the dispersion relation for the frequency of wave modes; and in order to examine the properties of those, we consider a particular case where bottom irregularities are cylinders of various heights and radii. It is demonstrated that if all irregularities are of the same height, h, there exist two topographic and one Rossby modes. The frequency of one of the topographic modes is ‘locked’ inside the band (−fh/2H0, fh/2H0), where f is the Coriolis parameter and H0 is the mean depth of the ocean. The frequencies of the other topographic mode and the barotropic Rossby mode are ‘locked’ above and below the band, respectively. It is also demonstrated that if the heights of cylinders are distributed within a certain range, (−h0, h0), no harmonic modes exist with frequencies inside the interval (−fh0/2H0, fh0/2H0). The topographic and Rossby modes are ‘pushed’ out of the ‘prohibited’ band.

Multi-Center Study of Thromboplastin Calibration Precision – Influence of Reagent Species, Composition, and International Sensitivity Index (ISI)

1993 ◽  
Vol 69 (01) ◽  
pp. 035-040 ◽  
Author(s):  
A M H P van den Besselaar ◽  
R M Bertina
Keyword(s):  
Oral Anticoagulants ◽  
International Normalized Ratio ◽  
The Other ◽  
World Health ◽  
Rabbit Brain ◽  
Sensitivity Index ◽  
Bovine Plasma ◽  
Significant Difference ◽  
The Mean ◽  
International Sensitivity Index

SummaryFour thromboplastin reagents were tested by 18 laboratories in Europe, North-America, and Australasia, according to a detailed protocol. One thromboplastin was the International Reference Preparation for ox brain thromboplastin combined with adsorbed bovine plasma (coded OBT/79), and the second was a certified reference material for rabbit brain thromboplastin, plain (coded CRM 149R). The other two thromboplastin reagents were another rabbit plain brain thromboplastin (RP) with a lower ISI than CRM 149R and a rabbit brain thromboplastin combined with adsorbed bovine plasma (RC). Calibration of the latter two reagents was performed according to methods recommended by the World Health Organization (W. H. O.).The purpose of this study was to answer the following questions: 1) Is the calibration of the RC reagent more precise against the bovine/combined (OBT/79) than against the rabbit/plain reagent (CRM 149R)? 2) Is the precision of calibration influenced by the magnitude of the International Sensitivity Index (ISI)?The lowest inter-laboratory variation of ISI was observed in the calibration of the rabbit/plain reagent (RP) against the other rabbit/plain reagent (CRM 149R) (CV 1.6%). The highest interlaboratory variation was obtained in the calibration of rabbit/plain (RP) against bovine/combined (OBT/79) (CV 5.1%). In the calibration of the rabbit/combined (RC) reagent, there was no difference in precision between OBT/79 (CV 4.3%) and CRM 149R (CV 4.2%). Furthermore, there was no significant difference in the precision of the ISI of RC obtained with CRM 149R (ISI = 1.343) and the rabbit/plain (RP) reagent with ISI = 1.14. In conclusion, the calibration of RC could be performed with similar precision with either OBT/79 or CRM 149R, or RP.The mean ISI values calculated with OBT/79 and CRM 149R were practically identical, indicating that there is no bias in the ISI of these reference preparations and that these reference preparations have been stable since their original calibration studies in 1979 and 1987, respectively.International Normalized Ratio (INR) equivalents were calculated for a lyophilized control plasma derived from patients treated with oral anticoagulants. There were small but significant differences in the mean INR equivalents between the bovine and rabbit thromboplastins. There were no differences in the interlaboratory variation of the INR equivalents, when the four thromboplastins were compared.

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