331 research outputs found
Phase and frequency entrainment in locally coupled phase oscillators with repulsive interactions
Recent experiments in one and two-dimensional microfluidic arrays of droplets
containing Belousov -Zhabotinsky reactants show a rich variety of spatial
patterns [J. Phys. Chem. Lett. 1, 1241-1246 (2010)]. The dominant coupling
between these droplets is inhibitory. Motivated by this experimental system, we
study repulsively coupled Kuramoto oscillators with nearest neighbor
interactions, on a linear chain as well as a ring in one dimension, and on a
triangular lattice in two dimensions. In one dimension, we show using linear
stability analysis as well as numerical study, that the stable phase patterns
depend on the geometry of the lattice. We show that a transition to the ordered
state does not exist in the thermodynamic limit. In two dimensions, we show
that the geometry of the lattice constrains the phase difference between two
neighbouring oscillators to 120 degrees. We report the existence of domains
with either clockwise or anti-clockwise helicity, leading to defects in the
lattice. We study the time dependence of these domains and show that at large
coupling strengths, the domains freeze due to frequency synchronization.
Signatures of the above phenomena can be seen in the spatial correlation
functions.Comment: 9 pages, 12 figure
Segregation of Polymers in Confined Spaces
We investigate the motion of two overlapping polymers with self-avoidance
confined in a narrow 2d box. A statistical model is constructed using blob
free-energy arguments. We find spontaneous segregation under the condition: , and mixing under , where L is the length of the box, and
the polymer extension in an infinite slit. Segregation time scales are
determined by solving a mean first-passage time problem, and by performing
Monte Carlo simulations. Predictions of the two methods show good agreement.
Our results may elucidate a driving force for chromosomes segregation in
bacteria
Shapes of Semiflexible Polymers in Confined Spaces
We investigate the conformations of a semiflexible polymer confined to a
square box. Results of Monte Carlo simulations show the existence of a shape
transition when the persistence length of the polymer becomes comparable to the
dimensions of box. An order parameter is introduced to quantify this behavior.
A simple mean-field model is constructed to study the effect of the shape
transition on the effective persistence length of the polymer.Comment: 8 pages, 20 figure
A linear programming-based method for job shop scheduling
We present a decomposition heuristic for a large class of job shop scheduling problems. This heuristic utilizes information from the linear programming formulation of the associated optimal timing problem to solve subproblems, can be used for any objective function whose associated optimal timing problem can be expressed as a linear program (LP), and is particularly effective for objectives that include a component that is a function of individual operation
completion times. Using the proposed heuristic framework, we address job shop scheduling problems with a variety of objectives where intermediate holding costs need to be explicitly considered. In computational testing, we demonstrate the performance of our proposed solution approach
Glassy Dynamics in a Frustrated Spin System: Role of Defects
In an effort to understand the glass transition, the kinetics of a spin model
with frustration but no quenched randomness has been analyzed. The
phenomenology of the spin model is remarkably similiar to that of structural
glasses. Analysis of the model suggests that defects play a major role in
dictating the dynamics as the glass transition is approached.Comment: 9 pages, 5 figures, accepted in J. Phys.: Condensed Matter,
proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics
Fatal bilateral pneumonitis after locoregional thoracic chemoradiation in a transplanted patient under immunosuppressive therapy
Background: After thoracic radiotherapy a pneumonitis may occur, mostly confined to the irradiated volume of the lung. In general, it resolves spontaneously without long-term effects. Case Report: A 68-year-old man was diagnosed with a stage IIIA adenocarcinoma of the lung and was treated with sequential chemoradiation. He had a heart and kidney transplant for which an immunosuppressant was taken. During the fourth week of radiotherapy, he developed a bilateral interstitial pneumonia. Despite antibiotics and steroids, the patient died twelve days after the onset of complaints due to respiratory failure. Autopsy showed in all pulmonary lobes extensive diffuse alveolar damage, probably leading to respiratory insufficiency and death. Literature and Conclusion: Bilateral pneumonitis after radiotherapy is thought to be an immunologically-mediated response, which usually resolves without long-term effects. Since in radiation pneumonitis an increase in T-cells is described, the suppression of these cells by an immunosuppressant might have exaggerated the pulmonary toxicity
Effects of Multiphase Gas and Projection on X-ray Observables in Simulated Galaxy Clusters as Seen by eROSITA
The number density of galaxy clusters as a function of mass and redshift is a
sensitive function of the cosmological parameters. To use clusters for
cosmological parameter studies, it is necessary to determine their masses as
accurately as possible, which is typically done via mass-observable scaling
relations. X-ray observables can be biased by multiphase gas and projection
effects, especially in the case where cluster temperatures and luminosities are
estimated from single-model fits to all of the emission with a given radius.
Using simulated galaxy clusters from a realistic cosmological simulation, we
seek to determine the importance of these biases in the context of
Spectrum-Roentgen-Gamma/eROSITA observations of clusters. We extract clusters
from the Magneticum suite, and simulate eROSITA observations of these clusters
using PHOX and SIXTE. We compare the fitted observables from these observations
to those derived from the simulations. We fitted an intrinsically scattered
scaling relation to these measurements following a Bayesian
approach with which we fully took into account the selection effects and the
mass function. The largest biases on the cluster observables come from the
inadequacy of single-temperature model fits to represent emission from
multiphase gas, as well as a bias arising from cluster emission within the
projected along the line of sight but outside of the spherical
. We find that the biases on temperature and luminosity due to the
projection of emission from other clusters within is small. We find
that our simulated clusters follow a scaling relation that has a
broadly consistent but slightly shallower slope compared to the literature, and
that the intrinsic scatter of at given T is lower compared to the
recent observational results where the selection effects are fully considered.Comment: 18 pages, 17 figures, accepted by A&
Effective Field Theory of the Zero-Temperature Triangular-Lattice Antiferromagnet: A Monte Carlo Study
Using a Monte Carlo coarse-graining technique introduced by Binder et al., we
have explicitly constructed the continuum field theory for the zero-temperature
triangular Ising antiferromagnet. We verify the conjecture that this is a
gaussian theory of the height variable in the interface representation of the
spin model. We also measure the height-height correlation function and deduce
the stiffness constant. In addition, we investigate the nature of defect-defect
interactions at finite temperatures, and find that the two-dimensional Coulomb
gas scenario applies at low temperatures.Comment: 26 pages, 9 figure
Kinetics of Ordering in Fluctuation-Driven First-Order Transitions: Simulations and Dynamical Renormalization
Many systems where interactions compete with each other or with constraints
are well described by a model first introduced by Brazovskii. Such systems
include block copolymers, alloys with modulated phases, Rayleigh-Benard Cells
and type-I superconductors. The hallmark of this model is that the fluctuation
spectrum is isotropic and has a minimum at a nonzero wave vector represented by
the surface of a d-dimensional hyper-sphere. It was shown by Brazovskii that
the fluctuations change the free energy structure from a to a
form with the disordered state metastable for all quench depths.
The transition from the disordered to the periodic, lamellar structure changes
from second order to first order and suggests that the dynamics is governed by
nucleation. Using numerical simulations we have confirmed that the equilibrium
free energy function is indeed of a form. A study of the dynamics,
however, shows that, following a deep quench, the dynamics is described by
unstable growth rather than nucleation. A dynamical calculation, based on a
generalization of the Brazovskii calculations shows that the disordered state
can remain unstable for a long time following the quench.Comment: 18 pages, 15 figures submitted to PR
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