51,199 research outputs found
Fluctuations and universality in a catalysis model with long-range reactivity
The critical properties of the Ziff-Gulari-Barshad (ZGB) model with the
addition of long-range reactivity [C.H. Chan and P.A. Rikvold, Phys. Rev. E 91,
012103 (2015)] are further investigated. The scaling behaviors of the order
parameter, susceptibility, and correlation length provide addi- tional evidence
that the universality class of the ZGB system changes from the two-dimensional
Ising class to the mean-field class with the addition of even a weak long-range
reactivity mechanism
Gravastars and Black Holes of Anisotropic Dark Energy
Dynamical models of prototype gravastars made of anisotropic dark energy are
constructed, in which an infinitely thin spherical shell of a perfect fluid
with the equation of state divides the whole spacetime
into two regions, the internal region filled with a dark energy fluid, and the
external Schwarzschild region. The models represent "bounded excursion" stable
gravastars, where the thin shell is oscillating between two finite radii, while
in other cases they collapse until the formation of black holes. Here we show,
for the first time in the literature, a model of gravastar and formation of
black hole with both interior and thin shell constituted exclusively of dark
energy. Besides, the sign of the parameter of anisotropy () seems to
be relevant to the gravastar formation. The formation is favored when the
tangential pressure is greater than the radial pressure, at least in the
neighborhood of the isotropic case ().Comment: 16 pages, 8 figures. Accepted for publication in Gen. Rel. Gra
Instability of three dimensional conformally dressed black hole
The three dimensional black hole solution of Einstein equations with negative
cosmological constant coupled to a conformal scalar field is proved to be
unstable against linear circularly symmetric perturbations.Comment: 5 pages, REVTe
Bolometric light curves of supernovae and post-explosion magnetic fields
The various effects leading to diversity in the bolometric light curves of
supernovae are examined: nucleosynthesis, kinematic differences, ejected mass,
degree of mixing, and configuration and intensity of the magnetic field are
discussed. In Type Ia supernovae, a departure in the bolometric light curve
from the full-trapping decline of Co can occur within the two and a half
years after the explosion, depending on the evolutionary path followed by the
WD during the accretion phase. If convection has developed in the WD core
during the presupernova evolution, starting several thousand years before the
explosion, a tangled magnetic field close to the equipartition value should
have grown in the WD. Such an intense magnetic field would confine positrons
where they originate from the Co decays, and preclude a strong departure
from the full-trapping decline, as the supernova expands. This situation is
expected to occur in C+O Chandrasekhar WDs as opposed to edge-lit detonated
sub-Chandrasekhar WDs. If the pre-explosion magnetic field of the WD is less
intense than 10G, a lack of confinement of the positrons emitted in the
Co decay and a departure from full-trapping decline would occur. The
time at which it takes place can provide estimates of the original magnetic
field of the WD, its configuration, and also of the mass of the supernova
ejecta. In SN 1991bg, the bolometric light curve suggests absence of a
significant tangled magnetic field (intensity lower than G).
Chandrasekhar-mass models do not reproduce the bolometric light curve of this
supernova. For SN 1972E, on the contrary, there is evidence for a tangled
configuration of the magnetic field and its light curve is well reproduced by a
Chandrasekhar WD explosion.Comment: 54 pages, including 8 figures. To appear in Ap
Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV gamma ray emission
We present the implementation and the first results of cosmic ray (CR)
feedback in the Feedback In Realistic Environments (FIRE) simulations. We
investigate CR feedback in non-cosmological simulations of dwarf, sub-
starburst, and galaxies with different propagation models, including
advection, isotropic and anisotropic diffusion, and streaming along field lines
with different transport coefficients. We simulate CR diffusion and streaming
simultaneously in galaxies with high resolution, using a two moment method. We
forward-model and compare to observations of -ray emission from nearby
and starburst galaxies. We reproduce the -ray observations of dwarf and
galaxies with constant isotropic diffusion coefficient . Advection-only and streaming-only
models produce order-of-magnitude too large -ray luminosities in dwarf
and galaxies. We show that in models that match the -ray
observations, most CRs escape low-gas-density galaxies (e.g.\ dwarfs) before
significant collisional losses, while starburst galaxies are CR proton
calorimeters. While adiabatic losses can be significant, they occur only after
CRs escape galaxies, so they are only of secondary importance for -ray
emissivities. Models where CRs are ``trapped'' in the star-forming disk have
lower star formation efficiency, but these models are ruled out by -ray
observations. For models with constant that match the -ray
observations, CRs form extended halos with scale heights of several kpc to
several tens of kpc.Comment: 31 pages, 26 figures, accepted for publication in MNRA
Secondary organic aerosol formation from photooxidation of naphthalene and alkylnaphthalenes: implications for oxidation of intermediate volatility organic compounds (IVOCs)
Current atmospheric models do not include secondary
organic aerosol (SOA) production from gas-phase reactions
of polycyclic aromatic hydrocarbons (PAHs). Recent
studies have shown that primary emissions undergo oxidation
in the gas phase, leading to SOA formation. This
opens the possibility that low-volatility gas-phase precursors
are a potentially large source of SOA. In this work,
SOA formation from gas-phase photooxidation of naphthalene,
1-methylnaphthalene (1-MN), 2-methylnaphthalene (2-
MN), and 1,2-dimethylnaphthalene (1,2-DMN) is studied in
the Caltech dual 28-m^3 chambers. Under high-NO_x conditions
and aerosol mass loadings between 10 and 40μgm^(−3),
the SOA yields (mass of SOA per mass of hydrocarbon reacted)
ranged from 0.19 to 0.30 for naphthalene, 0.19 to 0.39
for 1-MN, 0.26 to 0.45 for 2-MN, and constant at 0.31 for
1,2-DMN. Under low-NO_x conditions, the SOA yields were
measured to be 0.73, 0.68, and 0.58, for naphthalene, 1-
MN, and 2-MN, respectively. The SOA was observed to be
semivolatile under high-NO_x conditions and essentially nonvolatile
under low-NO_x conditions, owing to the higher fraction
of ring-retaining products formed under low-NO_x conditions.
When applying these measured yields to estimate
SOA formation from primary emissions of diesel engines
and wood burning, PAHs are estimated to yield 3–5 times
more SOA than light aromatic compounds over photooxidation
timescales of less than 12 h. PAHs can also account for
up to 54% of the total SOA from oxidation of diesel emissions,
representing a potentially large source of urban SOA
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