3,255 research outputs found
Cosmological Implications of the Fundamental Relations of X-ray Clusters
Based on the two-parameter family nature of X-ray clusters of galaxies
obtained in a separate paper, we discuss the formation history of clusters and
cosmological parameters of the universe. Utilizing the spherical collapse model
of cluster formation, and assuming that the cluster X-ray core radius is
proportional to the virial radius at the time of the cluster collapse, the
observed relations among the density, radius, and temperature of clusters imply
that cluster formation occurs in a wide range of redshift. The observed
relations favor the low-density universe. Moreover, we find that the model of
is preferable.Comment: 7 pages, 4 figures. To be published in ApJ Letter
Mass-Temperature Relation of Galaxy Clusters: A Theoretical Study
Combining conservation of energy throughout nearly-spherical collapse of
galaxy clusters with the virial theorem, we derive the mass-temperature
relation for X-ray clusters of galaxies . The normalization factor
and the scatter of the relation are determined from first principles with
the additional assumption of initial Gaussian random field. We are also able to
reproduce the recently observed break in the M-T relation at T \sim 3 \keV,
based on the scatter in the underlying density field for a low density
CDM cosmology. Finally, by combining observational data of high
redshift clusters with our theoretical formalism, we find a semi-empirical
temperature-mass relation which is expected to hold at redshifts up to unity
with less than 20% error.Comment: 43 pages, 13 figures, One figure is added and minor changes are made.
Accepted for Publication in Ap
Normalizing the Temperature Function of Clusters of Galaxies
We re-examine the constraints which can be robustly obtained from the
observed temperature function of X-ray cluster of galaxies. The cluster mass
function has been thoroughly studied in simulations and analytically, but a
direct simulation of the temperature function is presented here for the first
time. Adaptive hydrodynamic simulations using the cosmological Moving Mesh
Hydro code of Pen (1997a) are used to calibrate the temperature function for
different popular cosmologies. Applying the new normalizations to the
present-day cluster abundances, we find for a hyperbolic universe, and for a spatially flat universe with a cosmological constant.
The simulations followed the gravitational shock heating of the gas and dark
matter, and used a crude model for potential energy injection by supernova
heating. The error bars are dominated by uncertainties in the heating/cooling
models. We present fitting formulae for the mass-temperature conversions and
cluster abundances based on these simulations.Comment: 20 pages incl 5 figures, final version for ApJ, corrected open
universe \gamma relation, results unchange
Weak Lensing as a Calibrator of the Cluster Mass-Temperature Relation
The abundance of clusters at the present epoch and weak gravitational lensing
shear both constrain roughly the same combination of the power spectrum
normalization sigma_8 and matter energy density Omega_M. The cluster constraint
further depends on the normalization of the mass-temperature relation.
Therefore, combining the weak lensing and cluster abundance data can be used to
accurately calibrate the mass-temperature relation. We discuss this approach
and illustrate it using data from recent surveys.Comment: Matches the version in ApJL. Equation 4 corrected. Improvements in
the analysis move the cluster contours in Fig1 slightly upwards. No changes
in the conclusion
Matrix Quantization of Turbulence
Based on our recent work on Quantum Nambu Mechanics \cite{af2}, we provide
an explicit quantization of the Lorenz chaotic attractor through the
introduction of Non-commutative phase space coordinates as Hermitian matrices in . For the volume preserving part, they satisfy the
commutation relations induced by one of the two Nambu Hamiltonians, the second
one generating a unique time evolution. Dissipation is incorporated quantum
mechanically in a self-consistent way having the correct classical limit
without the introduction of external degrees of freedom. Due to its volume
phase space contraction it violates the quantum commutation relations. We
demonstrate that the Heisenberg-Nambu evolution equations for the Matrix Lorenz
system develop fast decoherence to N independent Lorenz attractors. On the
other hand there is a weak dissipation regime, where the quantum mechanical
properties of the volume preserving non-dissipative sector survive for long
times.Comment: 14 pages, Based on invited talks delivered at: Fifth Aegean Summer
School, "From Gravity to Thermal Gauge theories and the AdS/CFT
Correspondance", September 2009, Milos, Greece; the Intern. Conference on
Dynamics and Complexity, Thessaloniki, Greece, 12 July 2010; Workshop on
"AdS4/CFT3 and the Holographic States of Matter", Galileo Galilei Institute,
Firenze, Italy, 30 October 201
Controle preventivo do tombamento em mudas de cebola (Allium cepa L.).
bitstream/item/72338/1/CPAMN-COM.-TEC.-5-92.pd
Constraining Omega with Cluster Evolution
We show that the evolution of the number density of rich clusters of galaxies
breaks the degeneracy between Omega (the mass density ratio of the universe)
and sigma_{8} (the normalization of the power spectrum), sigma_{8}Omega^{0.5}
\simeq 0.5, that follows from the observed present-day abundance of rich
clusters. The evolution of high-mass (Coma-like) clusters is strong in Omega=1,
low-sigma_{8} models (such as the standard biased CDM model with sigma_{8}
\simeq 0.5), where the number density of clusters decreases by a factor of \sim
10^{3} from z = 0 to z \simeq 0.5; the same clusters show only mild evolution
in low-Omega, high-sigma_{8} models, where the decrease is a factor of \sim 10.
This diagnostic provides a most powerful constraint on Omega. Using
observations of clusters to z \simeq 0.5-1, we find only mild evolution in the
observed cluster abundance. We find Omega = 0.3 \pm 0.1 and sigma_{8} = 0.85
\pm 0.15 (for Lambda = 0 models; for Omega + Lambda = 1 models, Omega = 0.34
\pm 0.13). These results imply, if confirmed by future surveys, that we live in
a low-den sity, low-bias universe.Comment: 14 pages, 3 Postscript figures, ApJ Letters, accepte
Entropy and Poincar\'e recurrence from a geometrical viewpoint
We study Poincar\'e recurrence from a purely geometrical viewpoint. We prove
that the metric entropy is given by the exponential growth rate of return times
to dynamical balls. This is the geometrical counterpart of Ornstein-Weiss
theorem. Moreover, we show that minimal return times to dynamical balls grow
linearly with respect to its length. Finally, some interesting relations
between recurrence, dimension, entropy and Lyapunov exponents of ergodic
measures are given.Comment: 11 pages, revised versio
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