10,611 research outputs found
Dynamical heterogeneity in a highly supercooled liquid: Consistent calculations of correlation length, intensity, and lifetime
We have investigated dynamical heterogeneity in a highly supercooled liquid
using molecular-dynamics simulations in three dimensions. Dynamical
heterogeneity can be characterized by three quantities: correlation length
, intensity , and lifetime . We evaluated
all three quantities consistently from a single order parameter. In a previous
study (H. Mizuno and R. Yamamoto, Phys. Rev. E {\bf 82}, 030501(R) (2010)), we
examined the lifetime in two time intervals
and , where is the
-relaxation time and is the time at which the
non-Gaussian parameter of the Van Hove self-correlation function is maximized.
In the present study, in addition to the lifetime , we
evaluated the correlation length and the intensity from
the same order parameter used for the lifetime . We
found that as the temperature decreases, the lifetime
grows dramatically, whereas the correlation length and the intensity
increase slowly compared to or plateaus.
Furthermore, we investigated the lifetime in more
detail. We examined the time-interval dependence of the lifetime
and found that as the time interval increases,
monotonically becomes longer and plateaus at the
relaxation time of the two-point density correlation function. At the large
time intervals for which plateaus, the heterogeneous
dynamics migrate in space with a diffusion mechanism, such as the particle
density.Comment: 12pages, 13figures, to appear in Physical Review
Catalogue of 12CO(J=1-0) and 13CO(J=1-0) Molecular Clouds in the Carina Flare Supershell
We present a catalogue of 12CO(J=1-0) and 13CO(J=1-0) molecular clouds in the
spatio-velocity range of the Carina Flare supershell, GSH 287+04-17. The data
cover a region of ~66 square degrees and were taken with the NANTEN 4m
telescope, at spatial and velocity resolutions of 2.6' and 0.1 km/s.
Decomposition of the emission results in the identification of 156 12CO clouds
and 60 13CO clouds, for which we provide observational and physical parameters.
Previous work suggests the majority of the detected mass forms part of a
comoving molecular cloud complex that is physically associated with the
expanding shell. The cloud internal velocity dispersions, degree of
virialization and size-linewidth relations are found to be consistent with
those of other Galactic samples. However, the vertical distribution is heavily
skewed towards high-altitudes. The robust association of high-z molecular
clouds with a known supershell provides some observational backing for the
theory that expanding shells contribute to the support of a high-altitude
molecular layer.Comment: To be published in PASJ Vol. 60, No. 6. (Issued on December 25th
2008). 35 pages (including 13 pages of tables), 7 figures. Please note that
formatting problems with the journal macro result in loss of rightmost data
columns in some long tables. These will be fixed in the final published
issue. In the meantime, please contact the authors for missing dat
Cosmological Dynamics of a Dirac-Born-Infeld field
We analyze the dynamics of a Dirac-Born-Infeld (DBI) field in a cosmological
set-up which includes a perfect fluid. Introducing convenient dynamical
variables, we show the evolution equations form an autonomous system when the
potential and the brane tension of the DBI field are arbitrary power-law or
exponential functions of the DBI field. In particular we find scaling solutions
can exist when powers of the field in the potential and warp-factor satisfy
specific relations. A new class of fixed-point solutions are obtained
corresponding to points which initially appear singular in the evolution
equations, but on closer inspection are actually well defined. In all cases, we
perform a phase-space analysis and obtain the late-time attractor structure of
the system. Of particular note when considering cosmological perturbations in
DBI inflation is a fixed-point solution where the Lorentz factor is a finite
large constant and the equation of state parameter of the DBI field is .
Since in this case the speed of sound becomes constant, the solution can
be thought to serve as a good background to perturb about.Comment: 24 pages, 7 figures, minor corrections, references adde
Smc5/6 maintains stalled replication forks in a recombination-competent conformation
The Smc5/6 structural maintenance of chromosomes complex is required for efficient homologous recombination (HR). Defects in Smc5/6 result in chromosome missegregation and fragmentation. By characterising two Schizosaccharomyces pombe smc6 mutants, we define two separate functions for Smc5/6 in HR. The first represents the previously described defect in processing recombination-dependent DNA intermediates when replication forks collapse, which leads to increased rDNA recombination. The second novel function defines Smc5/6 as a positive regulator of recombination in the rDNA and correlates mechanistically with a requirement to load RPA and Rad52 onto chromatin genome-wide when replication forks are stably stalled by nucleotide depletion. Rad52 is required for all HR repair, but Rad52 loading in response to replication fork stalling is unexpected and does not correlate with damage-induced foci. We propose that Smc5/6 is required to maintain stalled forks in a stable recombination-competent conformation primed for replication restart
The gas temperature in the surface layers of protoplanetary disks
Models for the structure of protoplanetary disks have so far been based on
the assumption that the gas and the dust temperature are equal. The gas
temperature, an essential ingredient in the equations of hydrostatic
equilibrium of the disk, is then determined from a continuum radiative transfer
calculation, in which the continuum opacity is provided by the dust. It has
been long debated whether this assumption still holds in the surface layers of
the disk, where the dust infrared emission features are produced. In this paper
we compute the temperature of the gas in the surface layers of the disk in a
self-consistent manner. The gas temperature is determined from a
heating-cooling balance equation in which processes such as photoelectric
heating, dissociative heating, dust-gas thermal heat exchange and line cooling
are included. The abundances of the dominant cooling species such as CO, C, C+
and O are determined from a chemical network based on the atomic species H, He,
C, O, S, Mg, Si, Fe (Kamp & Bertoldi 2000). The underlying disk models to our
calculations are the models of Dullemond, van Zadelhoff & Natta (2002). We find
that in general the dust and gas temperature are equal to withing 10% for A_V
>~ 0.1, which is above the location of the `super-heated surface layer' in
which the dust emission features are produced (e.g. Chiang & Goldreich 1997).
High above the disk surface the gas temperature exceeds the dust temperature
and can can become -- in the presence of polycyclic aromatic hydrocarbons -- as
high as 600 K at a radius of 100 AU. This is a region where CO has fully
dissociated, but a significant fraction of hydrogen is still in molecular form.
The densities are still high enough for non-negligible H_2 emission to be
produced.....(see paper for full abstract)Comment: 28 pages, 8 figures, accepted for publication in Ap
Particle Acceleration, Magnetic Field Generation, and Associated Emission in Collisionless Relativistic Jets
Nonthermal radiation observed from astrophysical systems containing
relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray
bursts (GRBs), and Galactic microquasar systems usually have power-law emission
spectra. Recent PIC simulations using injected relativistic electron-ion
(electro-positron) jets show that acceleration occurs within the downstream
jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., the Buneman instability,
other two-streaming instability, and the Weibel instability) created in the
shocks are responsible for particle (electron, positron, and ion) acceleration.
The simulation results show that the Weibel instability is responsible for
generating and amplifying highly nonuniform, small-scale magnetic fields. These
magnetic fields contribute to the electron's transverse deflection behind the
jet head. The ``jitter'' radiation from deflected electrons has different
properties than synchrotron radiation which assumes a uniform magnetic field.
This jitter radiation may be important to understanding the complex time
evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and
supernova remnants.Comment: 4 pages, 3 figures, contributed talk at the workshop: High Energy
Phenomena in Relativistic Outflows (HEPRO), Dublin, 24-28 September 2007.
Fig. 3 is replaced by the correct versio
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