1,565 research outputs found
Dual characterization of critical fluctuations: Density functional theory & nonlinear dynamics close to a tangent bifurcation
We improve on the description of the relationship that exists between
critical clusters in thermal systems and intermittency near the onset of chaos
in low-dimensional systems. We make use of the statistical-mechanical language
of inhomogeneous systems and of the renormalization group (RG) method in
nonlinear dynamics to provide a more accurate, formal, approach to the subject.
The description of this remarkable correspondence encompasses, on the one hand,
the density functional formalism, where classical and quantum mechanical
analogues match the procedure for one-dimensional clusters, and, on the other,
the RG fixed-point map of functional compositions that captures the essential
dynamical behavior. We provide details of how the above-referred theoretical
approaches interrelate and discuss the implications of the correspondence
between the high-dimensional (degrees of freedom) phenomenon and
low-dimensional dynamics.Comment: 8 figure
High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX
We have mapped the NGC 2023 reflection nebula in [CII] and CO(11--10) with
the heterodyne receiver GREAT on SOFIA and obtained slightly smaller maps in
13CO(3--2), CO(3--2), CO(4--3), CO(6--5), and CO(7--6) with APEX in Chile. We
use these data to probe the morphology, kinematics, and physical conditions of
the C II region, which is ionized by FUV radiation from the B2 star HD37903.
The [CII] emission traces an ellipsoidal shell-like region at a position angle
of ~ -50 deg, and is surrounded by a hot molecular shell. In the southeast,
where the C II region expands into a dense, clumpy molecular cloud ridge, we
see narrow and strong line emission from high-J CO lines, which comes from a
thin, hot molecular shell surrounding the [CII] emission. The [CII] lines are
broader and show photo evaporating gas flowing into the C II region. Based on
the strength of the [13CII] F=2--1 line, the [CII] line appears to be somewhat
optically thick over most of the nebula with an optical depth of a few. We
model the physical conditions of the surrounding molecular cloud and the PDR
emission using both RADEX and simple PDR models. The temperature of the CO
emitting PDR shell is ~ 90 -- 120 K, with densities of 10^5 -- 10^6 cm^-3, as
deduced from RADEX modeling. Our PDR modeling indicates that the PDR layer
where [CII] emission dominates has somewhat lower densities, 10^4 to a few
times 10^5 cm^-3Comment: Accepted by A&
Tunable entanglement distillation of spatially correlated down-converted photons
We report on a new technique for entanglement distillation of the bipartite
continuous variable state of spatially correlated photons generated in the
spontaneous parametric down-conversion process (SPDC), where tunable
non-Gaussian operations are implemented and the post-processed entanglement is
certified in real-time using a single-photon sensitive electron multiplying CCD
(EMCCD) camera. The local operations are performed using non-Gaussian filters
modulated into a programmable spatial light modulator and, by using the EMCCD
camera for actively recording the probability distributions of the
twin-photons, one has fine control of the Schmidt number of the distilled
state. We show that even simple non-Gaussian filters can be finely tuned to a
~67% net gain of the initial entanglement generated in the SPDC process.Comment: 12 pages, 6 figure
Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions
Using 2D particle-in-cell plasma simulations, we study electron acceleration by temperature anisotropy instabilities, assuming conditions typical of above-the-loop-top sources in solar flares. We focus on the long-term effect of Te,⊥ > Te,∥ instabilities by driving the anisotropy growth during the entire simulation time through imposing a shearing or a compressing plasma velocity (Te,⊥ and Te,∥ are the temperatures perpendicular and parallel to the magnetic field). This magnetic growth makes Te,⊥/Te,∥ grow due to electron magnetic moment conservation, and amplifies the ratio ωce/ωpe from ∼0.53 to ∼2 (ωce and ωpe are the electron cyclotron and plasma frequencies, respectively). In the regime ωce/ωpe ≲ 1.2–1.7, the instability is dominated by oblique, quasi-electrostatic modes, and the acceleration is inefficient. When ωce/ωpe has grown to ωce/ωpe ≳ 1.2–1.7, electrons are efficiently accelerated by the inelastic scattering provided by unstable parallel, electromagnetic z modes. After ωce/ωpe reaches ∼2, the electron energy spectra show nonthermal tails that differ between the shearing and compressing cases. In the shearing case, the tail resembles a power law of index αs ∼ 2.9 plus a high-energy bump reaching ∼300 keV. In the compressing runs, αs ∼ 3.7 with a spectral break above ∼500 keV. This difference can be explained by the different temperature evolutions in these two types of simulations, suggesting that a critical role is played by the type of anisotropy driving, ωce/ωpe, and the electron temperature in the efficiency of the acceleration
Numerical simulation of tsunami runup in northern Chile based on non-uniform k −2 slip distributions
ArtÃculo de publicación ISIA large seismic gap lies along northern Chile and could potentially trigger a M (w) similar to 8.8-9.0 megathrust earthquake as pointed out in several studies. The April 1, 2014, Pisagua earthquake broke the middle segment of the megathrust. Some slip models suggest that it ruptured mainly from a depth of 30 to 55 km along dip and over 180 km in length, reaching a magnitude M (w) 8.1-8.2. The northern and southern segments are still unbroken; thus, there is still a large area that could generate a M (w) > 8.5 earthquake with a strong tsunami. To better understand the effects of source parameters on the impact of a tsunami in the near field, as a case study, we characterize earthquake size for a hypothetical and great seismic event, M (w) 9.0, in northern Chile. On the basis of physical earthquake source models, we generate stochastic k (-2) finite fault slips taking into account the non-planar geometry of the megathrust in northern Chile. We analyze a series of random slip models and compute vertical co-seismic static displacements by adding up the displacement field from all point sources distributed over a regular grid mesh on the fault. Under the assumption of passive generation, the tsunami numerical model computes the runup along the shore. The numerical results show a maximum peak-runup of similar to 35-40 m in the case of some heterogeneous slip models. Instead, the minimum runup along the coast, from the heterogeneous slip models tested, almost coincides with the runup computed from the uniform slip model. This latter assumption underestimates the runup by a factor of similar to 6 at some places along the coast, showing agreement with near-field runups calculated by other authors using similar methodologies, but applied in a different seismotectonic context. The statistical estimate of empirical cumulative distribution functions conducted on two subsets of slips, and their respective runups, shows that slip models with large amount of slip near the trench are more probable to produce higher runups than the other subset. The simple separation criterion was to choose slip models that concentrate at least 60 % of the total seismic moment in the upper middle part of the non-planar rupture fault.Conicyt (Comision Nacional de Ciencia y Tecnologia) under Grant Fondecyt
113063
Abundant Z-cyanomethanimine in the interstellar medium: paving the way to the synthesis of adenine
We report the first detection in the interstellar medium of the Z-isomer of
cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We
identified six transitions of Z-cyanomethanimine, along with five transitions
of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Center
quiescent molecular cloud G+0.693. The Z-isomer has a column density of
(2.00.6)10 cm and an abundance of
1.510. The relative abundance ratio between the isomers is
[Z/E]6. This value cannot be explained by the two chemical formation
routes previously proposed (gas-phase and grain surface), which predicts
abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good
agreement with thermodynamic equilibrium at the gas kinetic temperature
(130210 K). Since isomerization is not possible in the ISM, the two species
may be formed at high temperature. New chemical models, including surface
chemistry on dust grains and gas-phase reactions, should be explored to explain
our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN
shows that precursors of adenine are efficiently formed in the ISM.Comment: Accepted in Monthly Notices of the Royal Astronomical Society Letter
Complex organic molecules in the Galactic Centre: the N-bearing family
We present an unbiased spectral line survey toward the Galactic Centre (GC)
quiescent giant molecular cloud (QGMC), G+0.693 using the GBT and IRAM 30
telescopes. Our study highlights an extremely rich organic inventory of
abundant amounts of nitrogen (N)-bearing species in a source without signatures
of star formation. We report the detection of 17 N-bearing species in this
source, of which 8 are complex organic molecules (COMs). A comparison of the
derived abundances relative to H is made across various galactic and
extragalactic environments. We conclude that the unique chemistry in this
source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays
also playing an important role in the chemistry. Like previous findings
obtained for O-bearing molecules, our results for N-bearing species suggest a
more efficient hydrogenation of these species on dust grains in G+0.693 than in
hot cores in the Galactic disk, as a consequence of the low dust temperatures
coupled with energetic processing by X-ray/cosmic ray radiation in the GC.Comment: 24 pages, 23 figures, 7 tables, accepted for publication in MNRA
Chemical Features in the Circumnuclear Disk of the Galactic Center
The circumnuclear disk (CND) of the Galactic Center is exposed to many
energetic phenomena coming from the supermassive black hole Sgr A* and stellar
activities. These energetic activities can affect the chemical composition in
the CND by the interaction with UV-photons, cosmic-rays, X-rays, and shock
waves. We aim to constrain the physical conditions present in the CND by
chemical modeling of observed molecular species detected towards it. We
analyzed a selected set of molecular line data taken toward a position in the
southwest lobe of the CND with the IRAM 30m and APEX 12-meter telescopes and
derived the column density of each molecule using a large velocity gradient
(LVG) analysis. The determined chemical composition is compared with a
time-dependent gas-grain chemical model based on the UCL\_CHEM code that
includes the effects of shock waves with varying physical parameters. Molecules
such as CO, HCN, HCO, HNC, CS, SO, SiO, NO, CN, HCO, HCN,
NH and HO are detected and their column densities are obtained.
Total hydrogen densities obtained from LVG analysis range between and cm and most species indicate values around
several cm, which are lower than values corresponding to
the Roche limit, which shows that the CND is tidally unstable. The chemical
models show good agreement with the observations in cases where the density is
cm, the cosmic-ray ionization rate is high, s, or shocks with velocities km s have occurred.
Comparison of models and observations favors a scenario where the cosmic-ray
ionization rate in the CND is high, but precise effects of other factors such
as shocks, density structures, UV-photons and X-rays from the Sgr A* must be
examined with higher spatial resolution data.Comment: 17 Pages, 13 figures, accepted for publication in A&
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