15,248 research outputs found
Income Convergence Clubs for Brazilian Municipalities: A Non-Parametric Analysis (english version of WPE-6/2003)
Memory effects on the statistics of fragmentation
We investigate through extensive molecular dynamics simulations the
fragmentation process of two-dimensional Lennard-Jones systems. After
thermalization, the fragmentation is initiated by a sudden increment to the
radial component of the particles' velocities. We study the effect of
temperature of the thermalized system as well as the influence of the impact
energy of the ``explosion'' event on the statistics of mass fragments. Our
results indicate that the cumulative distribution of fragments follows the
scaling ansatz , where is
the mass, and are cutoff parameters, and is a scaling
exponent that is dependent on the temperature. More precisely, we show clear
evidence that there is a characteristic scaling exponent for each
macroscopic phase of the thermalized system, i.e., that the non-universal
behavior of the fragmentation process is dictated by the state of the system
before it breaks down.Comment: 5 pages, 8 figure
The XMM spectral catalog of SDSS optically selected Seyfert 2 galaxies
We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert
2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond
the local universe, using good quality X-ray spectra in combination with high
S/N optical spectra for their robust classification. We analyzed all available
XMM-Newton archival observations of narrow emission line galaxies that meet the
above criteria in the redshift range 0.05<z<0.35. We initially selected narrow
line AGN using the SDSS optical spectra and the BPT classification diagram. We
further modeled and removed the stellar continuum, and we analyzed the residual
emission line spectrum to exclude any possible intermediate-type Seyferts. Our
final catalog comprises 31 Sy2 galaxies with median redshift z~0.1. X-ray
spectroscopy is performed using the available X-ray spectra from the 3XMM and
the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find
seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick
classification agrees with other commonly used diagnostics, such as the X-ray
to mid-IR luminosity ratio and the X-ray to [OIII] luminosity ratio. Most
importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the
simplest unification model. Their accretion rates are significantly lower than
the rest of our Sy2 sample, in agreement with previous studies that predict the
absence of the broad line region below a certain Eddington ratio threshold.Comment: 12 pages, 6 figures, accepted for publication in A&
Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3 Gyr after the Big Bang
We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at z = 4.567, in order to better constrain the nature of the high-redshift end of the submillimeter-selected galaxy (SMG) population. We secured ^(12)CO molecular line detections for the J = 2 →1 and J = 5 →4 transitions using the Karl G. Jansky Very Large Array (VLA) and the NOrthern Extended Millimeter Array (NOEMA) interferometer. The broad (FWHM ~ 750 km s^(−1)) and tentative double-peaked profiles of the two ^(12)CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk, as previously revealed from [CII] 158 μm line observations. Based on the 12CO(2 →1) emission line, we derived L′_(CO)=(3.4±0.6)×10^(10) K km s^(−1) pc^2, which yields a molecular gas mass of M_(H2)(α_(CO)/4.3)=(1.5±0.3)×10^(11) M⊙ and unveils a gas-rich system with μ_(gas)(α_(CO)/4.3)≡M_(H2)/M⋆=3.3±0.7. The extreme star formation efficiency of AzTEC/C159, parametrized by the ratio L_(IR)/L′_(CO)=(216±80) L⊙ (K km s^(−1) pc^2)^(−1), is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies and SMGs. Likewise, the ^(12)CO(5 →4)/CO(2 →1) line brightness temperature ratio of r_(52)= 0.55 ± 0.15 is consistent with high-excitation conditions as observed in SMGs. Based on mass budget considerations, we constrained the value for the L′_(CO) – H_2 mass conversion factor in AzTEC/C159, that is, α_(CO)=3.9_(−1.3)^(+2.7) M⊙ K^(−1) km^(−1) s pc^(−2), which is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps and forms stars as efficiently as in merger-driven systems and generates high gas excitation. These results support the evolutionary connection between AzTEC/C159-like systems and massive quiescent disk galaxies at z ~ 2
Localization properties of a tight-binding electronic model on the Apollonian network
An investigation on the properties of electronic states of a tight-binding
Hamiltonian on the Apollonian network is presented. This structure, which is
defined based on the Apollonian packing problem, has been explored both as a
complex network, and as a substrate, on the top of which physical models can
defined. The Schrodinger equation of the model, which includes only nearest
neighbor interactions, is written in a matrix formulation. In the uniform case,
the resulting Hamiltonian is proportional to the adjacency matrix of the
Apollonian network. The characterization of the electronic eigenstates is based
on the properties of the spectrum, which is characterized by a very large
degeneracy. The rotation symmetry of the network and large number of
equivalent sites are reflected in all eigenstates, which are classified
according to their parity. Extended and localized states are identified by
evaluating the participation rate. Results for other two non-uniform models on
the Apollonian network are also presented. In one case, interaction is
considered to be dependent of the node degree, while in the other one, random
on-site energies are considered.Comment: 7pages, 7 figure
Teleparallel Equivalent of Non-Abelian Kaluza-Klein Theory
Based on the equivalence between a gauge theory for the translation group and
general relativity, a teleparallel version of the non-abelian Kaluza-Klein
theory is constructed. In this theory, only the fiber-space turns out to be
higher-dimensional, spacetime being kept always four-dimensional. The resulting
model is a gauge theory that unifies, in the Kaluza-Klein sense, gravitational
and gauge fields. In contrast to the ordinary Kaluza-Klein models, this theory
defines a natural length-scale for the compact sub-manifold of the fiber space,
which is shown to be of the order of the Planck length.Comment: Revtex4, 7 pages, no figures, to appear in Phys. Rev.
Importance of Granular Structure in the Initial Conditions for the Elliptic Flow
We show effects of granular structure of the initial conditions (IC) of
hydrodynamic description of high-energy nucleus-nucleus collisions on some
observables, especially on the elliptic-flow parameter v2. Such a structure
enhances production of isotropically distributed high-pT particles, making v2
smaller there. Also, it reduces v2 in the forward and backward regions where
the global matter density is smaller, so where such effects become more
efficacious.Comment: 4 pages, 5 figure
Efficient formalism for large scale ab initio molecular dynamics based on time-dependent density functional theory
A new "on the fly" method to perform Born-Oppenheimer ab initio molecular
dynamics (AIMD) is presented. Inspired by Ehrenfest dynamics in time-dependent
density functional theory, the electronic orbitals are evolved by a
Schroedinger-like equation, where the orbital time derivative is multiplied by
a parameter. This parameter controls the time scale of the fictitious
electronic motion and speeds up the calculations with respect to standard
Ehrenfest dynamics. In contrast to other methods, wave function orthogonality
needs not be imposed as it is automatically preserved, which is of paramount
relevance for large scale AIMD simulations.Comment: 5 pages, 3 color figures, revtex4 packag
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