Results 271 to 280 of about 5,390,161 (308)

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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Host density and the evolution of parasite virulence

Journal of Theoretical Biology, 1989
Social and cultural habits of human populations affect the biological evolution of the agents of infectious diseases. Measles and similar diseases have evolved in the Old World and cannot have existed in their present form before the rise of the great river valley civilizations.
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THE EVOLUTION OF THE DENSITY OPERATOR FOR DRIVEN SYSTEM

Acta Mathematica Scientia, 1999
The author presents a reformulation of subdynamics for the system driven by the Liouvillian \(L_0+\lambda L_I(t)\), where \(L_0\) is the time-independent unperturbed part of the Liouvillian and \(L_I\) the time-dependent perturbed one. The reformulation of subdynamics is necessary because it gives the explicit formulas to calculate the creation ...
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Time Evolution of the Probability Density

1992
The content of the preceding chapters was essentially devoted to the analysis of the first and second order moments of the state variable u = u(t,x,ω) at fixed values of the time t and space x variables. On the other hand, in the class of problems dealt with in this book, u is a time dependent random field and its behaviour can be properly described by
N. Bellomo, Z. Brzezniak, L. M. de Socio
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On the chemical evolution and densities of the planets

Geochimica et Cosmochimica Acta, 1959
It is assumed that planets have accreted at low temperature from a cloud of dust and gas of cosmic composition. Subsequent melting may cause reduction of metallic oxides by carbonaceous compounds which were trapped during accretion. The metal so produced would segregate and form a core.
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Ecology and Evolution of Density-Dependence

2020
In nature, ecological communities often consist of many species that are tightly coupled with others in diverse ecological relationships. This ecological complexity has attracted keen attention both in, but different between evolutionary biology and community ecology.
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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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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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On the Evolution of Density-Regulating Behavior

1987
Behavior that influences animal dispersion affects both the survival and reproduction of individuals and the dynamics of entire populations. In this chapter, I consider, from the perspective of individual selection, the evolution of behavior that directly influences dispersion.
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Evolution of the density for a chaotic map

Physics Letters A, 1984
Abstract For the discrete-time map xt+11 = 4xt(1−xt) an exact, explicit expression is given for the time-dependent density rt (x) evolving from a uniform initial density on (0,1). As t → ∞, rt(x) approaches the known invariant density r(x) = 1/[π x(1−x) ] .
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