2,638 research outputs found
The triple-mode pulsating variable V823 Cas
Based on extended multicolour CCD photometry of the triple-mode radial
pulsator V823 Cas we studied the properties of the coupling frequencies invoked
by nonlinear processes. Our results support that a resonance connection as
suggested by Antonello & Aikawa (1998) affects the mode coupling behaviour. The
P1/P0 period ratio of V823 Cas has an "out of range" value if compared with the
period ratios of the known double mode pulsators, while the P2/P1 period ratio
is normal. The periods and period ratios cannot be consistently interpret
without conflict with pulsation and/or evolution models. We attempt to
interpret this failure by the suggestion that at present, the periods of V823
Cas are in a transient, resonance affected state, thus do not reflect the true
parameters of the object. The anomalous period change behaviour of the
fundamental and second overtone modes supports this idea. We have also raised
the possibility that a f0 + f2 = 2f1 resonance may act in triple mode
pulsators.Comment: 10 pages, 7 figures, 5 tables. Accepted for publication in Astronomy
and Astrophysic
Time-Dependent Density Functional Theory for Driven Lattice Gas Systems with Interactions
We present a new method to describe the kinetics of driven lattice gases with
particle-particle interactions beyond hard-core exclusions. The method is based
on the time-dependent density functional theory for lattice systems and allows
one to set up closed evolution equations for mean site occupation numbers in a
systematic manner. Application of the method to a totally asymmetric site
exclusion process with nearest-neighbor interactions yields predictions for the
current-density relation in the bulk, the phase diagram of non-equilibrium
steady states and the time evolution of density profiles that are in good
agreement with results from kinetic Monte Carlo simulations.Comment: 11 pages, 3 figure
Power spectra of TASEPs with a localized slow site
The totally asymmetric simple exclusion process (TASEP) with a localized
defect is revisited in this article with attention paid to the power spectra of
the particle occupancy N(t). Intrigued by the oscillatory behaviors in the
power spectra of an ordinary TASEP in high/low density phase(HD/LD) observed by
Adams et al. (2007 Phys. Rev. Lett. 99 020601), we introduce a single slow site
with hopping rate q<1 to the system. As the power spectrum contains
time-correlation information of the particle occupancy of the system, we are
particularly interested in how the defect affects fluctuation in particle
number of the left and right subsystems as well as that of the entire system.
Exploiting Monte Carlo simulations, we observe the disappearance of
oscillations when the defect is located at the center of the system. When the
defect is off center, oscillations are restored. To explore the origin of such
phenomenon, we use a linearized Langevin equation to calculate the power
spectrum for the sublattices and the whole lattice. We provide insights into
the interactions between the sublattices coupled through the defect site for
both simulation and analytical results.Comment: 16 pages, 6 figures; v2: Minor revision
Two-Channel Totally Asymmetric Simple Exclusion Processes
Totally asymmetric simple exclusion processes, consisting of two coupled
parallel lattice chains with particles interacting with hard-core exclusion and
moving along the channels and between them, are considered. In the limit of
strong coupling between the channels, the particle currents, density profiles
and a phase diagram are calculated exactly by mapping the system into an
effective one-channel totally asymmetric exclusion model. For intermediate
couplings, a simple approximate theory, that describes the particle dynamics in
vertical clusters of two corresponding parallel sites exactly and neglects the
correlations between different vertical clusters, is developed. It is found
that, similarly to the case of one-channel totally asymmetric simple exclusion
processes, there are three stationary state phases, although the phase
boundaries and stationary properties strongly depend on inter-channel coupling.
An extensive computer Monte Carlo simulations fully support the theoretical
predictions.Comment: 13 pages, 10 figure
Distribution of dwell times of a ribosome: effects of infidelity, kinetic proofreading and ribosome crowding
Ribosome is a molecular machine that polymerizes a protein where the sequence
of the amino acid residues, the monomers of the protein, is dictated by the
sequence of codons (triplets of nucleotides) on a messenger RNA (mRNA) that
serves as the template. The ribosome is a molecular motor that utilizes the
template mRNA strand also as the track. Thus, in each step the ribosome moves
forward by one codon and, simultaneously, elongates the protein by one amino
acid. We present a theoretical model that captures most of the main steps in
the mechano-chemical cycle of a ribosome. The stochastic movement of the
ribosome consists of an alternating sequence of pause and translocation; the
sum of the durations of a pause and the following translocation is the time of
dwell of the ribosome at the corresponding codon. We derive the analytical
expression for the distribution of the dwell times of a ribosome in our model.
Whereever experimental data are available, our theoretical predictions are
consistent with those results. We suggest appropriate experiments to test the
new predictions of our model, particularly, the effects of the quality control
mechanism of the ribosome and that of their crowding on the mRNA track.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Physical Biology. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at DOI:10.1088/1478-3975/8/2/02600
Understanding the edge effect in TASEP with mean-field theoretic approaches
We study a totally asymmetric simple exclusion process (TASEP) with one
defect site, hopping rate , near the system boundary. Regarding our system
as a pair of uniform TASEP's coupled through the defect, we study various
methods to match a \emph{finite} TASEP and an \emph{infinite} one across a
common boundary. Several approximation schemes are investigated. Utilizing the
finite segment mean-field (FSMF) method, we set up a framework for computing
the steady state current as a function of the entry rate and
. For the case where the defect is located at the entry site, we obtain an
analytical expression for which is in good agreement with Monte
Carlo simulation results. When the defect is located deeper in the bulk, we
refined the scheme of MacDonald, et.al. [Biopolymers, \textbf{6}, 1 (1968)] and
find reasonably good fits to the density profiles before the defect site. We
discuss the strengths and limitations of each method, as well as possible
avenues for further studies.Comment: 16 pages, 4 figure
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