This work focuses on the timing properties of accreting neutron stars and black holes in binary systems. It aims at development of the physical alternative to the commonplace ad hoc description of the Fourier power density spectrum of X-ray timing signal. We employ diffusion theory to directly solve for X-ray luminosity fluctuations. The basic underlying physical assumption is that the observed variability of X-ray luminosity originates as the result of local fluctuations of the mass accretion rate, at all radii in the disk, that diffusively propagate outward. Suggested diffusion model of the power spectrum formation operates with parameters that are physical characteristics of the accretion flow: the diffusion time scale, Reynolds number of the flow (which is connected to the viscosity alpha-parameter), Keplerian and magnetosonic oscillation frequencies, radial size of the transition layer, and viscosity index, related to the viscosity distribution law in the system. These quantities constitute the core of temporal data used along with the spectral information to study physics of accretion.

One of the remarkable phenomena, characterizing both Galactic and extra-Galactic Xray binary systems, is the substantial variability of a photon ux, detectable in a very broad range of timescales. For instance, the accretion ow near a black hole event horizon can produce X-ray variability on a millisecond timescale. At the same time aperiodic changes from the extended accretion disk formed around the same black hole can occur on timescales of order of several months to years. A complex structure, involving high and low frequency nearly periodic oscillations and aperiodic features, observed in X-ray lightcurves, is the subject of intensive studies. The characteristic quantities, extracted from temporal analysis, carry speci c physical meaning and contain direct observational information about dynamics of the accreting X-ray source. It is the established fact that X-ray spectral and timing properties are tightly correlated. Combined together, the photon energy spectrum and the power density spectrum analyses, form a powerful framework that brings up the complete (in the energy/space domain) picture of the physical processes at work in the accreting system. Simultaneous study of spectral and timing characteristics allows for comprehensive probing of the geometry of accretion ows, reliable identification of the type of an X-ray source (black hole vs neutron star), constraining mass, size, and spin of accreting stellar-mass compact objects. Up until now there is no self-consistent physical model of the formation and evolution of the X-ray variability. This leaves a relative freedom in interpretation of the characteristic quantities obtained from the timing analysis. The current work aims at development of the physical alternative to the commonplace ad hoc description of the Fourier power density spectrum of X-ray timing signal. In the following study we employ the diffusion theory to directly solve for the X-ray luminosity fluctuations. The basic underlying physical assumption is that the observed variability of X-ray luminosity originates as the result of local fluctuations of the accretion rate, at all radii in the disk, that diffusively propagate outward. Energy dissipation (and X-ray emission) occurs in a narrow, shock-like region, called the transition layer, where the Keplerian ow becomes non-Keplerian in order to adjust itself to the slowly-rotating surface of a neutron star or the innermost stable orbit around a black hole. The X-ray time signal from the transition region, as seen by a remote observer, is obtained by integrating over the emission zone. The signal's power spectrum is then calculated and analyzed. Our diffusion model of the power spectrum formation operates with parameters that are physical characteristics of the accretion ow: the diffusion time scale, the Reynolds number (which is connected to the viscosity -parameter), Keplerian and magnetosonic quasi-periodic oscillation frequencies, radial size of the transition layer, and viscosity index, related to the viscosity distribution law in the system. These quantities constitute the core of temporal data used along with the spectral information to study physics of accretion. The proposed propagating fluctuation model can reproduce fundamental properties of the variability observed in X-ray light curves of accreting black hole and neutron star systems, as well as explain the power spectrum evolution during the spectral state transitions of the source.

Provides a comprehensive summary on the physical models and current theory of black hole accretion, growth and mergers, in both the supermassive and stellar-mass cases. This title reviews in-depth research on accretion on all scales, from galactic binaries to intermediate mass and supermassive black holes. Possible future directions of accretion are also discussed. The following main themes are covered: a historical perspective; physical models of accretion onto black holes of all masses; black hole fundamental parameters; and accretion, jets and outflows. An overview and outlook on the topic is also presented. This volume summarizes the status of the study of astrophysical black hole research and is aimed at astrophysicists and graduate students working in this field. Originally published in Space Science Reviews, Vol 183/1-4, 2014.

This volume serves as a general introduction to the state of the art of quantitatively characterizing chaotic and turbulent behavior. It is the outgrowth of an international workshop on "Quantitative Measures of Dynamical Complexity and Chaos" held at Bryn Mawr College, June 22-24, 1989. The workshop was co-sponsored by the Naval Air Development Center in Warminster, PA and by the NATO Scientific Affairs Programme through its special program on Chaos and Complexity. Meetings on this subject have occurred regularly since the NATO workshop held in June 1983 at Haverford College only two kilometers distant from the site of this latest in the series. At that first meeting, organized by J. Gollub and H. Swinney, quantitative tests for nonlinear dynamics and chaotic behavior were debated and promoted [1). In the six years since, the methods for dimension, entropy and Lyapunov exponent calculations have been applied in many disciplines and the procedures have been refined. Since then it has been necessary to demonstrate quantitatively that a signal is chaotic rather than it being acceptable to observe that "it looks chaotic". Other related meetings have included the Pecos River Ranch meeting in September 1985 of G. Mayer Kress [2) and the reflective and forward looking gathering near Jerusalem organized by M. Shapiro and I. Procaccia in December 1986 [3). This meeting was proof that interest in measuring chaotic and turbulent signals is widespread.

The formation of galaxies is one of the greatest puzzles in astronomy, the solution is shrouded in the depths of space and time, but has profound implications for the universe we observe today. This book discusses the beginnings of the process from cosmological observations and calculations. It examines the different theories of galaxy formation and shows where each theory either succeeds or fails in explaining what we actually observe. In addition, the book looks ahead to what we may expect to uncover about the epoch of galaxy formation from the new and upcoming generations of telescopes and technology.

Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.