scholarly journals Bayesian Inference Applied to Pulsar’s Models

2017 ◽  
Vol 45 ◽  
pp. 1760038
Author(s):  
Rubens M. Marinho ◽  
Heitor O. de Oliveira ◽  
Nadja S. Magalhães ◽  
Rodolfo Valentim ◽  
Jaziel G. Coelho ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Bayesian Inference ◽  
Angular Velocity ◽  
Bayesian Statistics ◽  
Posterior Distribution ◽  
Bayes Factor ◽  
Velocity Versus ◽  
Best Fit ◽  
The Magnetic Field

The goal of this work is to apply Bayesian statistics to the problem of pulsars in order to compute the Bayes factor and investigate which one among different EoS could better fit known pulsar data, regarding the rate of decrease of the angular velocity versus the angular velocity itself. We also find the posterior distribution and the best fit for some relevant parameters of the pulsar like the mass and the magnetic field.

scholarly journals Solar wind and substorm excitation of the wavy current sheet

2009 ◽  
Vol 27 (6) ◽  
pp. 2457-2474 ◽  
Author(s):  
C. Forsyth ◽  
M. Lester ◽  
R. C. Fear ◽  
E. Lucek ◽  
I. Dandouras ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Current Sheet ◽  
Pressure Pulse ◽  
Wind Pressure ◽  
Expansion Velocity ◽  
Solar Wind Pressure ◽  
Wave Models ◽  
Best Fit ◽  
The Magnetic Field

Abstract. Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002). We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005) and Erkaev et al. (2008). We find that the Erkaev et al. (2008) model gives the best fit to the observations.

scholarly journals An In-Class Demonstration of Bayesian Inference

2019 ◽  
Author(s):  
Johnny van Doorn ◽  
Dora Matzke ◽  
Eric-Jan Wagenmakers
Keyword(s):  
Bayesian Inference ◽  
Posterior Distribution ◽  
Prior Distribution ◽  
Sequential Analysis ◽  
Bayes Factor ◽  
Classroom Setting ◽  
Key Concepts

Sir Ronald Fisher's venerable experiment "The Lady Tasting Tea'' is revisited from a Bayesian perspective. We demonstrate how a similar tasting experiment, conducted in a classroom setting, can familiarize students with several key concepts of Bayesian inference, such as the prior distribution, the posterior distribution, the Bayes factor, and sequential analysis.

Why only a small fraction of quasars are radio loud?

2018 ◽  
Vol 14 (S342) ◽  
pp. 201-204
Author(s):  
Xinwu Cao
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Angular Momentum ◽  
Angular Velocity ◽  
Strong Magnetic Field ◽  
Weak Magnetic Field ◽  
Thin Disk ◽  
Relativistic Jets ◽  
Jet Formation ◽  
The Magnetic Field

AbstractIt is still a mystery why only a small fraction of quasars contain relativistic jets. A strong magnetic field is a necessary ingredient for jet formation. Gas falls from the Bondi radius RB nearly freely to the circularization radius Rc, and a thin accretion disk is formed within Rc We suggest that the external weak magnetic field threading interstellar medium is substantially enhanced in this region, and the magnetic field at Rc can be sufficiently strong to drive outflows from the disk if the angular velocity of the gas is low at RB. In this case, the magnetic field is efficiently dragged in the disk, because most angular momentum of the disk is removed by the outflows that lead to a significantly high radial velocity. The strong magnetic field formed in this way may accelerate jets in the region near the black hole, either by the Blandford-Payne or/and Blandford-Znajek mechanisms. If the angular velocity of the circumnuclear gas is low, the field advection in the thin disk is inefficient, and it will appear as a radio-quiet (RQ) quasar.

Experimental Study Noise of HMR2003 Sensor with or without the Use of Amplifier AMP04

2014 ◽  
Vol 605 ◽  
pp. 629-632 ◽  
Author(s):  
N. Hadjigeorgiou
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Angular Velocity ◽  
Rotation Angle ◽  
Magnetic Sensors ◽  
Successful Attempt ◽  
Wear Measurement ◽  
The Magnetic Field

Magnetic sensors offer many essential benefits: they enable contactless and thus without wear measurement of mechanical amounts of such as the rotation angle and angular velocity. And are a powerful and economical solution. In this work became a successful attempt to detect and record the noise of a Anisotropic Magnetoresistors (AMR) sensor, hte HMC2003, which manufactured by Honeywell Inc. was tested for its ability to detect the magnetic field and as well as how the corruption, which are involved due to the noise.

Hydromagnetic wavelike instabilities in a rapidly rotating stratified fluid

1973 ◽  
Vol 61 (3) ◽  
pp. 609-624 ◽  
Author(s):  
D. J. Acheson
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Growth Rates ◽  
Homogeneous Model ◽  
Stratified Fluid ◽  
Generation Mechanism ◽  
Helmholtz Instability ◽  
Coaxial Cylinders ◽  
The Magnetic Field ◽  
Rotating Stratified Fluid

We examine the hydromagnetic stability of a radially stratified fluid rotating between two coaxial cylinders, with particular emphasis on the case when the angular velocity greatly exceeds both buoyant and Alfvén frequencies. If the magnetic field is predominantly azimuthal instabilities then have an essentially non-axisymmetric and wavelike character. Various bounds on their phase speeds and growth rates are derived, including a ‘quadrant’ theorem analogous to Howard's semicircle theorem for Kelvin–Helmholtz instability. Their strong tendency to propagate against the basic rotation (i.e. ‘westward’), previously noted by the author in the study of a more simplified (homogeneous) model, seems relatively insensitive to the generation mechanism (e.g. unstable gradient of magnetic field, angular velocity or density), but a number of counterexamples show that this constraint need not apply if the magnetic field displays significant spatial variations of direction as well as magnitude and that eastward-propagating amplifying modes are then possible.

scholarly journals A Spectroscqpic Study of the Bp-Star θ Aur

1986 ◽  
Vol 90 ◽  
pp. 295-298
Author(s):  
D. Kolev ◽  
E. Georgeva
Keyword(s):  
Magnetic Field ◽  
Magnetic Dipole ◽  
Spectral Variability ◽  
Great Uncertainty ◽  
Field Geometry ◽  
Best Fit ◽  
The Magnetic Field

AbstractThe atmosphere parameters, spectral variability and the magnetic field geometry of the Bp-star θ Aur are evaluated from 30 coude-spectrograms. We adopt Te = 10 800K and lgg = 3.40 (with lower reliability of lg g ) . The equivalent widths of the metalic lines show a relatively great scattering which troubles the period search. The best fit to our data gives the period P = 3.620d, but the variability is clearly seen only for Sill lines. The uncertainties in the star parameters obtained bring to a great uncertainty in the magnetic dipole geometry: i = 86° + 39° and β = 18° + 80°. We adopt the most plausible star parameters to be: R = 3.8R⊙ M = 3.5R⊙, i = 80°, β = 20°, Bp = 1 KGs.

scholarly journals An In-Class Demonstration of Bayesian Inference

2019 ◽  
Vol 19 (1) ◽  
pp. 36-45
Author(s):  
Johnny van Doorn ◽  
Dora Matzke ◽  
Eric-Jan Wagenmakers
Keyword(s):  
Bayesian Inference ◽  
Posterior Distribution ◽  
Prior Distribution ◽  
Sequential Analysis ◽  
Bayes Factor ◽  
Classroom Setting ◽  
Key Concepts

Sir Ronald Fisher’s venerable experiment “The Lady Tasting Tea” is revisited from a Bayesian perspective. We demonstrate how a similar tasting experiment, conducted in a classroom setting, can familiarize students with several key concepts of Bayesian inference, such as the prior distribution, the posterior distribution, the Bayes factor, and sequential analysis.

Effects of porosity, profile of thickness, and angular acceleration on the magneto-electro-elastic behavior of a porous FGMEE rotating disc placed in a constant magnetic field

2020 ◽  
pp. 095440622093840 ◽  
Author(s):  
M Saadatfar ◽  
MH Zarandi ◽  
M Babaelahi
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Differential Equations ◽  
Lorentz Force ◽  
Angular Acceleration ◽  
Functionally Graded ◽  
Elastic Behavior ◽  
Shooting Methods ◽  
Rotating Disc ◽  
The Magnetic Field

Effects of porosity, profile of thickness and angular deceleration on the stress and deformation of a fluid-saturated functionally graded porous magneto-electro-elastic rotating disc are investigated in this article. Since the angular velocity is taken to be variable, the disc is subjected to Lorentz force in two directions: radial and circumferential. It is assumed that material properties of the disc obey power-law function of radius. The disc is uniformly porous and its thickness varies as a function of radius. First, three coupled governing partial differential equations in terms of the displacement and electric potential are converted to ordinary differential equations employing the separation of variable method. Then, obtained equations are solved using the Runge–Kutta and shooting methods for the case of fixed–free boundary condition. The effect of variable angular velocity, thickness profile, inhomogeneity index, porosity, and magnetic field is studied and illustrated graphically. The results demonstrate that considering angular acceleration for the disc has a considerable effect on the Lorentz force resulted from the magnetic field. Besides, the angular velocity constant has a significant effect on the stresses and displacements in the presence of the magnetic field.

Erklärung stellarer und planetarer Magnetfelder durch einen turbulenzbedingten Dynamomechanismus

1966 ◽  
Vol 21 (8) ◽  
pp. 1285-1296 ◽  
Author(s):  
M. Steenbeck ◽  
F. Krause
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Magnetic Fields ◽  
Cross Product ◽  
Skin Depth ◽  
Electrically Conducting ◽  
Magnetic Stars ◽  
The Magnetic Field ◽  
Component Parallel ◽  
Good Agreement

In a foregoing paper 1 the effects of a turbulent motion on magnetic fields were investigated. Especially turbulence was treated under the influence of CORIOLiS-forces and gradients of density and/or turbulence intensity. It was shown that on these conditions the average cross-product of velocity and magnetic field has a non-vanishing component parallel to the average magnetic field. Here we give the consequences of this effect for rotating, electrically conducting spheres.At first a sphere rotating with constant angular velocity is investigated. The quadratic effect provides for dynamo maintainance of the magnetic fields. A field of dipol-type has the weakest condition for maintainance. Applications to the magnetic field of the earth show a good agreement with the conceptions of the physical state of the earth’s core.For a second model differential rotation is included. We have also dynamo maintainance. Since we have to assume that generally the angular velocity is a function decreasing with the distance from the centre of the sphere, the calculations show that we have a preferred self-excited build-up of a quadrupol-type field. This model may be applicable to magnetic stars.Finally we look for dynamo maintainance of alternating fields. We consider the skin-depth to be small compared with the radius of the sphere, then we have plane geometry. The existence of periodical solutions is proved. Applications to the general magnetic field of the sun, which has a period of 22 years, are discussed.

POYNTING FLUX DOMINATED ACCRETION FLOW: A TWO-DIMENSIONAL MODEL

2006 ◽  
Vol 21 (03) ◽  
pp. 181-196
Author(s):  
HYUN KYU LEE
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Accretion Disk ◽  
Magnetic Surface ◽  
Energy Tensor ◽  
Two Dimensional ◽  
Accretion Flow ◽  
Poynting Flux ◽  
Stress Energy ◽  
The Magnetic Field

The dynamics of the accretion flow onto a black hole driven by Poynting flux is discussed in a simplified model of a two-dimensional accretion disk on equatorial plane. In an axisymmetric, stationary and force-free magnetosphere, the accretion flow is described by the three accretion equations obtained from the conservation of stress–energy tensor and one stream equation for a force-free magnetosphere. It is found that the angular velocity of the magnetic surface can be obtained by the dynamics of the accreting matter, [Formula: see text]. The effect of the magnetic field on the accretion flow is discussed in detail using the paraboloidal type configuration suggested by Blandford in 1976. In numerical analysis, it is demonstrated that the angular velocity of the disk, ΩD, deviates from the Keplerian angular velocity and the dynamics of the accretion disk is found to depend strongly on the ratio of the accretion rate to the magnetic field strength.

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