5,368 research outputs found
Pair-distribution functions of two-temperature two-mass systems: Comparison of MD, HNC, CHNC, QMC and Kohn-Sham calculations for dense hydrogen
Two-temperature, two-mass quasi-equilibrium plasmas may occur in electron-ion
plasmas,nuclear-matter, as well as in electron-hole condensed-matter systems.
Dense two-temperature hydrogen plasmas straddle the difficult partially -
degenerate regime of electron densities and temperatures which are important in
astrophysics, in inertial-confinement fusion research, and other areas of warm
dense matter physics. Results from Kohn-Sham calculations and QMC are used to
benchmark the procedures used in classical molecular-dynamics simulations, HNC
and CHNC methods to derive electron-electron and electron-proton pair -
distribution functions. Then, nonequilibrium molecular dynamics for two
-temperature, two-mass plasmas are used to obtain the pair distribution. Using
these results, the correct HNC and CHNC procedures for the evaluation of
pair-distribution functions in two-temperature two-mass two-component charged
fluids are established. Results for a mass ratio of 1:5, typical of
electron-hole fluids, as well as for compressed hydrogen are presented. PACS
Numbers: 52.25.Kn, 52.25Gj, 71.10.-w, 52.27.Gr, 26.30.+kComment: 17 pages, four figure
Disentangling the jet emission from protostellar systems. The ALMA view of VLA1623
Context: High-resolution studies of class 0 protostars represent the key to
constraining protostar formation models. VLA16234-2417 represents the prototype
of class 0 protostars, and it has been recently identified as a triple
non-coeval system. Aim: We aim at deriving the physical properties of the jets
in VLA16234-2417 using tracers of shocked gas. Methods: ALMA Cycle 0 Early
Science observations of CO(2-1) in the extended configuration are presented in
comparison with previous SMA CO(3-2) and Herschel-PACS [OI}] 63 micron
observations. Gas morphology and kinematics were analysed to constrain the
physical structure and origin of the protostellar outflows. Results: We reveal
a collimated jet component associated with the [OI] 63 micron emission at about
8'' (about 960 AU) from source B. This newly detected jet component is
inversely oriented with respect to the large-scale outflow driven by source A,
and it is aligned with compact and fast jet emission very close to source B
(about 0.3'') rather than with the direction perpendicular to the A disk. We
also detect a cavity-like structure at low projected velocities, which
surrounds the [OI] 63 micron emission and is possibly associated with the
outflow driven by source A. Finally, no compact outflow emission is associated
with source W. Conclusions: Our high-resolution ALMA observations seem to
suggest there is a fast and collimated jet component associated with source B.
This scenario would confirm that source B is younger than A, that it is in a
very early stage of evolution, and that it drives a faster, more collimated,
and more compact jet with respect to the large-scale slower outflow driven by
A. However, a different scenario of a precessing jet driven by A cannot be
firmly excluded from the present observations.Comment: Accepted for publication in Astronomy & Astrophysic
Exploring DCO as a tracer of thermal inversion in the disk around the Herbig Ae star HD163296
We aim to reproduce the DCO emission in the disk around HD163296 using a
simple 2D chemical model for the formation of DCO through the cold
deuteration channel and a parametric treatment of the warm deuteration channel.
We use data from ALMA in band 6 to obtain a resolved spectral imaging data cube
of the DCO =3--2 line in HD163296 with a synthesized beam of
0."53 0."42. We adopt a physical structure of the disk from the
literature that reproduces the spectral energy distribution. We then apply a
simplified chemical network for the formation of DCO that uses the physical
structure of the disk as parameters along with a CO abundance profile, a
constant HD abundance and a constant ionization rate. Finally, from the
resulting DCO abundances, we calculate the non-LTE emission using the 3D
radiative transfer code LIME. The observed DCO emission is reproduced by a
model with cold deuteration producing abundances up to .
Warm deuteration, at a constant abundance of , becomes
fully effective below 32 K and tapers off at higher temperatures, reproducing
the lack of DCO inside 90 AU. Throughout the DCO emitting zone a CO
abundance of is found, with 99\% of it frozen out below
19 K. At radii where both cold and warm deuteration are active, warm
deuteration contributes up to 20\% of DCO, consistent with detailed
chemical models. The decrease of DCO at large radii is attributed to a
temperature inversion at 250 AU, which raises temperatures above values where
cold deuteration operates. Increased photodesorption may also limit the radial
extent of DCO. The corresponding return of the DCO layer to the
midplane, together with a radially increasing ionization fraction, reproduces
the local DCO emission maximum at 260 AU.Comment: 9 pages, 5 figures, accepted 7th July 201
Wave spectra of 2D dusty plasma solids and liquids
Brownian dynamics simulations were carried out to study wave spectra of
two-dimensional dusty plasma liquids and solids for a wide range of
wavelengths. The existence of a longitudinal dust thermal mode was confirmed in
simulations, and a cutoff wavenumber in the transverse mode was measured.
Dispersion relations, resulting from simulations, were compared with those from
analytical theories, such as the random-phase approximation (RPA),
quasi-localized charged approximation (QLCA), and harmonic approximation (HA).
An overall good agreement between the QLCA and simulations was found for wide
ranges of states and wavelengths after taking into account the direct thermal
effect in the QLCA, while for the RPA and HA good agreement with simulations
were found in the high and low temperature limits, respectively.Comment: 26 pages, 9 figure
Temperature Relaxation in Hot Dense Hydrogen
Temperature equilibration of hydrogen is studied for conditions relevant to
inertial confinement fusion. New molecular-dynamics simulations and results
from quantum many-body theory are compared with Landau-Spitzer (LS) predictions
for temperatures T from 50 eV to 5000 eV, and densities with Wigner-Seitz radii
r_s = 1.0 and 0.5. The relaxation is slower than the LS result, even for
temperatures in the keV range, but converges to agreement in the high-T limit.Comment: 4 pages PRL style, two figure
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