The Experts below are selected from a list of 1629 Experts worldwide ranked by ideXlab platform
Frank H Shu - One of the best experts on this subject based on the ideXlab platform.
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collapse of magnetized singular isothermal toroids i the nonrotating case
The Astrophysical Journal, 2003Co-Authors: Anthony Allen, Frank H ShuAbstract:We study numerically the collapse of nonrotating self-gravitating magnetized singular isothermal toroids characterized by sound speed, a, and level of magnetic to thermal support, H0. In qualitative agreement with treatments by Galli & Shu and other workers, we find that the infalling material is deflected by the field lines toward the equatorial plane, creating a high-density flattened structure, a pseudodisk. The pseudodisk contracts dynamically in the radial direction, dragging the field lines and threading them into a highly pinched configuration that resembles a split monopole. The oppositely directed field lines across the midplane and the large implied stresses may play a role in how magnetic flux is lost in the actual situation in the presence of finite resistivity or ambipolar diffusion. The infall rate into the central regions is given to 5% uncertainty by the formula = (1 + H0)a3/G, where G is the Universal Gravitational Constant, anticipated by semianalytical studies of the self-similar Gravitational collapses of the singular isothermal sphere and isopedically magnetized disks. The introduction of finite initial rotation results in a complex interplay between pseudodisk and true (Keplerian) disk formation that is examined in a companion paper.
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collapse of magnetized singular isothermal toroids i non rotating case
arXiv: Astrophysics, 2003Co-Authors: Anthony Allen, Frank H ShuAbstract:We study numerically the collapse of non-rotating, self-gravitating, magnetized, singular isothermal toroids characterized by sound speed, $a$, and level of magnetic to thermal support, $H_0$. In qualitative agreement with previous treatments by Galli & Shu and other workers, we find that the infalling material is deflected by the field lines towards the equatorial plane, creating a high-density, flattened structure -- a pseudodisk. The pseudodisk contracts dynamically in the radial direction, dragging the field lines threading it into a highly pinched configuration that resembles a split monopole. The oppositely directed field lines across the midplane and the large implied stresses may play a role in how magnetic flux is lost in the actual situation in the presence of finite resistivity or ambipolar diffusion. The infall rate into the central regions is given to 5% uncertainty by the formula, $\dot M = (1+H_0)a^3/G$, where $G$ is the Universal Gravitational Constant, anticipated by semi-analytical studies of the self-similar Gravitational collapses of the singular isothermal sphere and isopedically magnetized disks. The introduction of finite initial rotation results in a complex interplay between pseudodisk and true (Keplerian) disk formation that is examined in a companion paper.
Jacobson D. L. - One of the best experts on this subject based on the ideXlab platform.
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Three Phase-Grating Moire Neutron Interferometer for Large Interferometer Area Applications
'American Physical Society (APS)', 2018Co-Authors: Sarenac Dusan, Pushin D. A., Huber M. G., Hussey D. S., Cory D. G., Cronin A. D., Miao Haixing, Arif Muhammad, Heacock Benjamin, Jacobson D. L.Abstract:We demonstrate a three phase-grating moire neutron interferometer in a highly intense neutron beam as a robust candidate for large area interferometry applications and for the characterization of materials. This novel far-field moire technique allows for broad wavelength acceptance and relaxed requirements related to fabrication and alignment, thus circumventing the main obstacles associated with perfect crystal neutron interferometry. We observed interference fringes with an interferometer length of 4 m and examined the effects of an aluminum 6061 alloy sample on the coherence of the system. Experiments to measure the autocorrelation length of samples and the Universal Gravitational Constant are proposed and discussed.U.S. Department of CommerceNational Institute of Standards and TechnologyCanada Excellence Research Chairs, Government of CanadaNatural Sciences and Engineering Research Council of CanadaU.S. Department of EnergyCanada First Research Excellence Fun
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Three Phase-Grating Moire Neutron Interferometer for Large Interferometer Area Applications
'American Physical Society (APS)', 2017Co-Authors: Sarenac D., Pushin D. A., Huber M. G., Hussey D. S., Miao H., Arif M., Cory D. G., Cronin A. D., Heacock B., Jacobson D. L.Abstract:We demonstrate a three phase-grating neutron interferometer as a robust candidate for large area interferometry applications and characterization of materials. This novel far-field moire technique allows for broad wavelength acceptance and relaxed requirements related to fabrication and alignment, circumventing the main obstacles associated with perfect crystal neutron interferometry. Interference fringes were observed with a total interferometer length of four meters, and the effects of an aluminum 6061 alloy sample on the coherence of the system was examined. Experiments to measure the autocorrelation length of samples and the Universal Gravitational Constant are proposed and discussed
Sergei M Kopeikin - One of the best experts on this subject based on the ideXlab platform.
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gravitomagnetic effects in the propagation of electromagnetic waves in variable Gravitational fields of arbitrary moving and spinning bodies
Physical Review D, 2002Co-Authors: Sergei M Kopeikin, Bahram MashhoonAbstract:Propagation of light in the Gravitational field of self-gravitating spinning bodies moving with arbitrary velocities is discussed. The Gravitational field is assumed to be weak everywhere. Equations of motion of a light ray are solved in the first post-Minkowskian approximation that is linear with respect to the Universal Gravitational Constant $G$. We do not restrict ourselves with the approximation of Gravitational lens so that the solution of light geodesics is applicable for arbitrary locations of source of light and observer. This formalism is applied for studying corrections to the Shapiro time delay in binary pulsars caused by the rotation of pulsar and its companion. We also derive the correction to the light deflection angle caused by rotation of gravitating bodies in the solar system (Sun, planets) or a Gravitational lens. The Gravitational shift of frequency due to the combined translational and rotational motions of light-ray-deflecting bodies is analyzed as well. We give a general derivation of the formula describing the relativistic rotation of the plane of polarization of electromagnetic waves (Skrotskii effect). This formula is valid for arbitrary translational and rotational motion of gravitating bodies and greatly extends the results of previous researchers. Finally, we discuss the Skrotskii effect for Gravitational waves emitted by localized sources such as a binary system. The theoretical results of this paper can be applied for studying various relativistic effects in microarcsecond space astrometry and developing corresponding algorithms for data processing in space astrometric missions such as FAME, SIM, and GAIA.
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lorentz covariant theory of light propagation in Gravitational fields of arbitrary moving bodies
Physical Review D, 1999Co-Authors: Sergei M Kopeikin, Gerhard SchaferAbstract:The Lorentz covariant theory of the propagation of light in the (weak) Gravitational fields of N-body systems consisting of arbitrarily moving pointlike bodies with Constant masses ${m}_{a}$ $(a=1,2,\dots{},N)$ is constructed. The theory is based on the Li\'enard-Wiechert representation of the metric tensor which describes a retarded type solution of the Gravitational field equations. A new approach for integrating the equations of motion of light particles (photons) depending on the retarded time argument is invented. Its application in the first post-Minkowskian approximation, which is linear with respect to the Universal Gravitational Constant G makes it evident that the equations of light propagation admit to be integrated straightforwardly by quadratures. Explicit expressions for the trajectory of a light ray and its tangent vector are obtained in algebraically closed form in terms of functionals of retarded time. General expressions for the relativistic time delay, the angle of light deflection, and the Gravitational shift of electromagnetic frequency are derived in the form of instantaneous functions of retarded time. They generalize previously known results for the case of static or uniformly moving bodies. The most important applications of the theory to relativistic astrophysics and astrometry are given. They include a discussion of the velocity-dependent terms in the Gravitational lens equation, the Shapiro time delay in binary pulsars, Gravitational Doppler shift, and a precise theoretical formulation of the general relativistic algorithms of data processing of radio and optical astrometric measurements made in the nonstationary Gravitational field of the solar system. Finally, proposals for future theoretical work being important for astrophysical applications are formulated.
Anthony Allen - One of the best experts on this subject based on the ideXlab platform.
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collapse of magnetized singular isothermal toroids i the nonrotating case
The Astrophysical Journal, 2003Co-Authors: Anthony Allen, Frank H ShuAbstract:We study numerically the collapse of nonrotating self-gravitating magnetized singular isothermal toroids characterized by sound speed, a, and level of magnetic to thermal support, H0. In qualitative agreement with treatments by Galli & Shu and other workers, we find that the infalling material is deflected by the field lines toward the equatorial plane, creating a high-density flattened structure, a pseudodisk. The pseudodisk contracts dynamically in the radial direction, dragging the field lines and threading them into a highly pinched configuration that resembles a split monopole. The oppositely directed field lines across the midplane and the large implied stresses may play a role in how magnetic flux is lost in the actual situation in the presence of finite resistivity or ambipolar diffusion. The infall rate into the central regions is given to 5% uncertainty by the formula = (1 + H0)a3/G, where G is the Universal Gravitational Constant, anticipated by semianalytical studies of the self-similar Gravitational collapses of the singular isothermal sphere and isopedically magnetized disks. The introduction of finite initial rotation results in a complex interplay between pseudodisk and true (Keplerian) disk formation that is examined in a companion paper.
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collapse of magnetized singular isothermal toroids i non rotating case
arXiv: Astrophysics, 2003Co-Authors: Anthony Allen, Frank H ShuAbstract:We study numerically the collapse of non-rotating, self-gravitating, magnetized, singular isothermal toroids characterized by sound speed, $a$, and level of magnetic to thermal support, $H_0$. In qualitative agreement with previous treatments by Galli & Shu and other workers, we find that the infalling material is deflected by the field lines towards the equatorial plane, creating a high-density, flattened structure -- a pseudodisk. The pseudodisk contracts dynamically in the radial direction, dragging the field lines threading it into a highly pinched configuration that resembles a split monopole. The oppositely directed field lines across the midplane and the large implied stresses may play a role in how magnetic flux is lost in the actual situation in the presence of finite resistivity or ambipolar diffusion. The infall rate into the central regions is given to 5% uncertainty by the formula, $\dot M = (1+H_0)a^3/G$, where $G$ is the Universal Gravitational Constant, anticipated by semi-analytical studies of the self-similar Gravitational collapses of the singular isothermal sphere and isopedically magnetized disks. The introduction of finite initial rotation results in a complex interplay between pseudodisk and true (Keplerian) disk formation that is examined in a companion paper.
Bahram Mashhoon - One of the best experts on this subject based on the ideXlab platform.
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gravitomagnetic effects in the propagation of electromagnetic waves in variable Gravitational fields of arbitrary moving and spinning bodies
Physical Review D, 2002Co-Authors: Sergei M Kopeikin, Bahram MashhoonAbstract:Propagation of light in the Gravitational field of self-gravitating spinning bodies moving with arbitrary velocities is discussed. The Gravitational field is assumed to be weak everywhere. Equations of motion of a light ray are solved in the first post-Minkowskian approximation that is linear with respect to the Universal Gravitational Constant $G$. We do not restrict ourselves with the approximation of Gravitational lens so that the solution of light geodesics is applicable for arbitrary locations of source of light and observer. This formalism is applied for studying corrections to the Shapiro time delay in binary pulsars caused by the rotation of pulsar and its companion. We also derive the correction to the light deflection angle caused by rotation of gravitating bodies in the solar system (Sun, planets) or a Gravitational lens. The Gravitational shift of frequency due to the combined translational and rotational motions of light-ray-deflecting bodies is analyzed as well. We give a general derivation of the formula describing the relativistic rotation of the plane of polarization of electromagnetic waves (Skrotskii effect). This formula is valid for arbitrary translational and rotational motion of gravitating bodies and greatly extends the results of previous researchers. Finally, we discuss the Skrotskii effect for Gravitational waves emitted by localized sources such as a binary system. The theoretical results of this paper can be applied for studying various relativistic effects in microarcsecond space astrometry and developing corresponding algorithms for data processing in space astrometric missions such as FAME, SIM, and GAIA.
