Results 211 to 220 of about 2,181,379 (230)

Space density evolution of quasars

Nature, 1978
ATTEMPTS to obtain interesting cosmological information from the study of quasars have been thwarted by the apparent large spread in quasar luminosities so that the conventional Hubble plot produces a scatter diagram1. Several authors2–4 have used an absolute magnitude–redshift diagram to provide a standard candle and hence improved the Hubble diagram.
N. J. STEWART, M. R. S. HAWKINS
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Microstructure evolution in density relaxation by tapping

Physical Review E, 2010
The density relaxation phenomenon is modeled using both Monte Carlo and discrete element simulations to investigate the effects of regular taps applied to a vessel having a planar floor filled with monodisperse spheres. Results suggest the existence of a critical tap intensity which produces a maximum bulk solids fraction.
Anthony D, Rosato, Oleksandr, Dybenko, David J, Horntrop, Vishagan, Ratnaswamy, Lou, Kondic   +4 more
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Evolution of the cosmic density matrix

Physical Review D, 1989
The dynamics of a reduced cosmic density matrix for minisuperspace is derived by projecting out inhomogeneous modes. This projection procedure roughly represents the intrinsic loss of information beyond the horizon of the local observer. Even if the wave function of the whole Universe exists, it will be unobservable and therefore should be projected ...
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Density Evolution for Expectation Propagation

2007 IEEE International Conference on Acoustics, Speech and Signal Processing - ICASSP '07, 2007
Expectation propagation (EP) is a theoretical extension of the belief propagation family of message passing algorithms for statistical inference which allows for efficient handling of models with continuous random variables as well as second or higher order correlation via the use of standard exponential families of probability measures.
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Evolution in Population Parameters: Density-Dependent Selection or Density-Dependent Fitness?

The American Naturalist, 2013
Density-dependent selection is one of earliest topics of joint interest to both ecologists and evolutionary biologists and thus occupies an important position in the histories of these disciplines. This joint interest is driven by the fact that density-dependent selection is the simplest form of feedback between an ecological effect of an organism's ...
Joseph, Travis, Jeff, Leips, F Helen, Rodd   +2 more
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Density Evolution Hypothesis for Quasars

Nature, 1966
ASSUMING that the red-shifts of quasars are cosmological, Longair1, and Roeder and Mitchell2, have suggested that the present available distribution of flux-densities at 178 Mc/s, S178, of quasars against red-shift implies that the radio luminosity, P, of quasars which exist at cosmic epoch t is a decreasing function of t.
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Social Subordination, Population Density, and Mammalian Evolution

Science, 1970
Natural selection, operating on phenotypic expressions of the genetic material, is generally held to be of fundamental importance in evolution. Natural selection includes environmental selection, by which is meant here the selection of particular correlated phenotypic-genotypic changes or adaptations that confer better survival, including competitive ...
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Density Stratification and Buoyancy Evolution in Pyroclastic Density Currents

Journal of Geophysical Research: Solid Earth
AbstractPyroclastic density currents (PDCs) are density‐stratified along their vertical axis, with the near‐bed portion being denser than the upper portion, resulting from particle settling and ambient air entrainment at current margins. Whereas vertical density stratification likely influences mixing, sedimentation, and buoyancy of PDCs, many depth ...
Sean B. O’Donnell, Blair A. Johnson, Eric C. P. Breard, James L. Buttles, James E. Gardner, David Mohrig, Josef Dufek   +6 more
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Density evolution and EXIT charts

2009
Introduction In Chapters 2–6 we introduced turbo, LDPC and RA codes and their iterative decoding algorithms. Simulation results show that these codes can perform extremely closely to Shannon's capacity limit with practical implementation complexity. In this chapter we analyze the performance of iterative decoders, determine how close they can in fact
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Density Matrices and Their Time Evolution

Open Systems & Information Dynamics, 2008
Already in the case of finite dimensional Hilbert spaces [Formula: see text] the general form of density matrices ρ is not known. The main reason for this lack of knowledge is the nonlinear constraint for these matrices. We propose a representation of density matrices on finite dimensional Hilbert spaces in terms of finitely many independent ...
E. Brüning, F. Petruccione
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