12,714 research outputs found
Influence of disordered porous media in the anomalous properties of a simple water model
The thermodynamic, dynamic and structural behavior of a water-like system
confined in a matrix is analyzed for increasing confining geometries. The
liquid is modeled by a two dimensional associating lattice gas model that
exhibits density and diffusion anomalies, in similarity to the anomalies
present in liquid water. The matrix is a triangular lattice in which fixed
obstacles impose restrictions to the occupation of the particles. We show that
obstacules shortens all lines, including the phase coexistence, the critical
and the anomalous lines. The inclusion of a very dense matrix not only suppress
the anomalies but also the liquid-liquid critical point
General approach for studying first-order phase transitions at low temperatures
By combining different ideas, a general and efficient protocol to deal with
discontinuous phase transitions at low temperatures is proposed. For small
's, it is possible to derive a generic analytic expression for appropriate
order parameters, whose coefficients are obtained from simple simulations. Once
in such regimes simulations by standard algorithms are not reliable, an
enhanced tempering method, the parallel tempering -- accurate for small and
intermediate system sizes with rather low computational cost -- is used.
Finally, from finite size analysis, one can obtain the thermodynamic limit. The
procedure is illustrated for four distinct models, demonstrating its power,
e.g., to locate coexistence lines and the phases density at the coexistence.Comment: 5 page
Diffusion anomaly and dynamic transitions in the Bell-Lavis water model
In this paper we investigate the dynamic properties of the minimal Bell-Lavis
(BL) water model and their relation to the thermodynamic anomalies. The
Bell-Lavis model is defined on a triangular lattice in which water molecules
are represented by particles with three symmetric bonding arms interacting
through van der Waals and hydrogen bonds. We have studied the model diffusivity
in different regions of the phase diagram through Monte Carlo simulations. Our
results show that the model displays a region of anomalous diffusion which lies
inside the region of anomalous density, englobed by the line of temperatures of
maximum density (TMD). Further, we have found that the diffusivity undergoes a
dynamic transition which may be classified as fragile-to-strong transition at
the critical line only at low pressures. At higher densities, no dynamic
transition is seen on crossing the critical line. Thus evidence from this study
is that relation of dynamic transitions to criticality may be discarded
Very extended cold gas, star formation and outflows in the halo of a bright QSO at z>6
Past observations of QSO host galaxies at z >6 have found cold gas and star
formation on compact scales of a few kiloparsecs. We present new high
sensitivity IRAM PdBI follow-up observations of the [CII] 158micron emission
line and FIR continuum in the host galaxy of SDSS J1148+5152, a luminous QSO at
redshift 6.4189. We find that a large fraction of the gas traced by [CII] is at
high velocities, up to ~1400 km/s relative to the systemic velocity, confirming
the presence of a major quasar-driven outflow indicated by previous
observations. The outflow has a complex morphology and reaches a maximum
projected radius of ~30 kpc. The extreme spatial extent of the outflow allows
us, for the first time in an external galaxy, to estimate mass-loss rate,
kinetic power and momentum rate of the outflow as a function of the projected
distance from the nucleus and the dynamical time-scale. These trends reveal
multiple outflow events during the past 100 Myr, although the bulk of the mass,
energy and momentum appear to have been released more recently, within the past
~20 Myr. Surprisingly, we discover that also the quiescent gas at systemic
velocity is extremely extended. More specifically, we find that, while 30% of
the [CII] within v\in(-200, 200) km/s traces a compact component that is not
resolved by our observations, 70% of the [CII] emission in this velocity range
is extended, with a projected FWHM size of 17.4+-1.4 kpc. We detect FIR
continuum emission associated with both the compact and the extended [CII]
components, although the extended FIR emission has a FWHM of 11+-3 kpc, thus
smaller than the extended [CII] source. Overall, our results indicate that the
cold gas traced by [CII] is distributed up to r~30 kpc. A large fraction of
extended [CII] is likely associated with star formation on large scales, but
the [CII] source extends well beyond the FIR continuum.Comment: Accepted for publication in A&A, 21 pages, 18 figures, 3 tables (v2:
accepted version, discussion expanded in Sect. 3, 4 and in the Appendices,
minor changes elsewhere
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