Gauge-invariant treatment of gravitational radiation near the source: Analysis and numerical simulations

1990 ◽  
Vol 42 (8) ◽  
pp. 2585-2594 ◽  
Author(s):  
Andrew M. Abrahams ◽  
Charles R. Evans
Keyword(s):  
Numerical Simulations ◽  
Gravitational Radiation ◽  
Source Analysis ◽  
Gauge Invariant

scholarly journals UNSTABLE MODES AND CONFINEMENT IN THE LATTICE SCHRÖDINGER FUNCTIONAL APPROACH

1998 ◽  
Vol 13 (11) ◽  
pp. 861-871 ◽  
Author(s):  
PAOLO CEA ◽  
LEONARDO COSMAI
Keyword(s):  
Gauge Theory ◽  
Numerical Simulations ◽  
Effective Action ◽  
Lattice Gauge Theory ◽  
Critical Length ◽  
Functional Approach ◽  
Gauge Invariant ◽  
Lattice Gauge ◽  
Chromomagnetic Field

We analyze the problem of the Nielsen–Olesen unstable modes in the SU(2) lattice gauge theory by means of a recently introduced gauge-invariant effective action. We perform numerical simulations in the case of a constant Abelian chromomagnetic field. We find that for lattice sizes above a certain critical length, the density of effective action shows a behavior compatible with the presence of the unstable modes. We put out a possible relation between the dynamics of the unstable modes and the confinement.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

Comparison of interictal EEG and MEG II: Loss of deep cortical fissures in polymicrogyria requires simultaneous EEG with MEG source analysis

2005 ◽  
Vol 36 (02) ◽  
Author(s):  
T Bast ◽  
G Ramantani ◽  
Ö Özkan ◽  
T Metzke ◽  
A Seitz ◽  
...  
Keyword(s):  
Source Analysis ◽  
Interictal Eeg
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