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Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 611 for “"Accretion"”.
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Accretion topics in astrophysics
Accretion theory is essential for understanding a multitude of varied astronomical observations such as X-ray binaries, active galactic nuclei and gamma-ray bursts. In this document three works on accretion will be presented.The first one is on the structure of an inviscid accretion disc with small …
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Black Hole Accretion Systems
"Accretion onto a black hole is the most efficient known process to convert gravitational energy into radiation. Some gamma-ray bursts (GRBs), some X-ray binaries, and all active galactic nuclei (AGN) are likely powered by accretion onto a rotating black hole. I model the global, timedependent …
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Magnetically torqued thin accretion disks
We consider geometrically thin accretion disks around millisecond X-ray pulsars. We start with the Shakura-Sunyaev thin disk model as a basis and modify the disk equations with a magnetic torque from the central neutron star. Disk solutions are computed for a range of neutron star magnetic fields. …
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The accretion of lower oceanic crust
… endmember theoretical models that describe the accretion of the lower oceanic crust at fast spreading rates. The first approach uses the record of hydrothermal alteration of the ocean crust, including Sr and O-isotopes, to investigate and quantify the role of hydrothermal circulation during the …
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Accretion by rotating magnetic neutron stars
… are rotating magnetic neutron stars undergoing accretion. The text of this thesis provides a historical introduction to four studies, contained herein as appendices, in which we develop a theory of accretion by such stars. In these studies, we first give a detailed magnetohydrodynamic …
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Accretion disks in the cataclysmic variables
The general equations describing the time-independent structure of gaseous circumstellar disks in vertical hydrostatic equilibrium are derived. The possibility of turbulent instablilty and the resulting viscosity laws are discussed.
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Surging Seepage: A Triple Bond Accretion System
… motion and frenetic energy. The work is an accretion of brightly colored biomorphic forms that extend out from the wall and onto the floor. Viscous parts ooze and drip while others are globular and bulbous. The hyper-organic forms suggest a paradoxical state of both ripening and rotting, …
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Resistive magnetohydrodynamic jets from protostellar accretion disks
Astrophysikalische Jets sind ausgedehnte, kollimierte Massenausflüsse von verschiedenen astronomischen Objekten. Zeitabhängige magnetohydrodynamische (MHD) Simulationen der Jet-Entwicklung müssen den Akrretionsprozess in der Scheibe berücksichtigen, da der Jet aus der Scheibenmaterie gespeist wird. …
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Time-dependent Accretion Flows onto Black Holes
Accretion onto compact objects plays a fundamental role in a number of astrophysical systems like active galactic nuclei (AGN) and black hole X-ray binaries (BHXB). The standard thin disk model fails to reproduce the spectra of these systems. They exhibit a blackbody-like component, generally …
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Measuring ice accretion with a microwave radiometer.
Ice accretion inside jet engines is a major threat to modern aviation. Ice crystals in the atmosphere can be ingested by turbofan jet engines and build up inside reducing airflow through the engine. A reliable method to detect ice inside the engine before power loss occurs is needed. A passive …
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Local Numerical Models of Turbulent Accretion Flows
… for driving angular momentum transport in accretion disks. This work provides a comprehensive study of MHD turbulent accretion flow using shearing box simulations.
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Hydrodynamic and Magnetohydrodynamic Convection in Accretion Disks
… of convection perpendicular to the plane of accretion disks have been discussed for several decades. Recent simulations combining convection and the magnetorotational instability have given fresh impetus to the debate, as the interplay of the two processes can enhance angular momentum …
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On the Dynamics of Noncircular Accretion Discs
The classical picture of an accretion disc is of a geometrically thin, nearly axisymmetric, fluid flow undergoing supersonic circular motion and slowly accreting due to angular momentum transport by the disc turbulence. There are, however, strong theoretical and observational grounds for …
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Disk Accretion to Rotating Magnetized Stars: Magnetohydrodynamic Simulations
… a rotating magnetized star and a surrounding accretion disk is a fundamental process in astrophysics, and is usually difficult to investigate due to the complicated magnetohydrodynamic structures. The aim of this work is for understanding the accretion manifestations of this interaction, …
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Shear instabilities between accretion disks and nova objects
… on the surface of white dwarfs caused by accretion from a companion star. Most studies focus on modelling the explosive phase (thermonuclear runaway), while this thesis, instead, focuses on the pre-explosion stage, investigating how shear instabilities and accretion-driven dynamics affect …
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A Numerical Study of Nonspherical Black Hole Accretion
… The aim is to study fully dynamic inviscid fluid accretion onto black holes, as well as to study the evolution and development of nonlinear instabilities in pressure supported accretion disks.
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Near-critical spherically symmetric accretion by neutron stars
Submitted by Carolyn Rauber (crauber2@illinois.edu) on 2012-01-24T20:23:01Z No. of bitstreams: 1 1993_fortner.pdf: 5017205 bytes, checksum: 1bb2f5533aab19fc255c0d3894022c3a (MD5)
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Studying Accretion Disc Winds with X-ray Spectroscopy
… results of my PhD research into the physics of accretion (infall) and ejection (outflow) of matter in compact objects. Accretion disc winds are formed of hot and ionised material launched by magnetic forces, radiation pressure or thermally from the discs of accretors. They have been discovered …
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Multiwavelength studies of accretion disks around compact objects
… for spectral flattening, and cannot rule out an accretion disk scenario for AXPs.
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Water and volatile element accretion to the inner planets
This thesis investigates the timing and source(s) of water and volatile elements to the inner solar system by studying the basaltic meteorites angrites and eucrites. In chapters 2 and 3, I present the results from angrite meteorites. Chapter 2 examines the water and volatile element content of the …
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