49,747 research outputs found
Symmetric Diblock Copolymers in Thin Films (I): Phase stability in Self-Consistent Field Calculations and Monte Carlo Simulations
We investigate the phase behavior of symmetric AB diblock copolymers confined
into a thin film. The film boundaries are parallel, impenetrable and attract
the A component of the diblock copolymer. Using a self-consistent field
technique [M.W. Matsen, J.Chem.Phys. {\bf 106}, 7781 (1997)], we study the
ordered phases as a function of incompatibility and film thickness in
the framework of the Gaussian chain model. For large film thickness and small
incompatibility, we find first order transitions between phases with different
number of lamellae which are parallel oriented to the film boundaries. At high
incompatibility or small film thickness, transitions between parallel oriented
and perpendicular oriented lamellae occur. We compare the self-consistent field
calculations to Monte Carlo simulations of the bond fluctuation model for chain
length N=32. In the simulations we quench several systems from to
and monitor the morphology into which the diblock copolymers
assemble. Three film thicknesses are investigated, corresponding to parallel
oriented lamellae with 2 and 4 interfaces and a perpendicular oriented
morphology. Good agreement between self-consistent field calculations and Monte
Carlo simulations is found.Comment: to appear in J.Chem.Phy
Interfaces between highly incompatible polymers of different stiffness: Monte Carlo simulations and self-consistent field calculations
We investigate interfacial properties between two highly incompatible
polymers of different stiffness. The extensive Monte Carlo simulations of the
binary polymer melt yield detailed interfacial profiles and the interfacial
tension via an analysis of capillary fluctuations. We extract an effective
Flory-Huggins parameter from the simulations, which is used in self-consistent
field calculations. These take due account of the chain architecture via a
partial enumeration of the single chain partition function, using chain
conformations obtained by Monte Carlo simulations of the pure phases. The
agreement between the simulations and self-consistent field calculations is
almost quantitative, however we find deviations from the predictions of the
Gaussian chain model for high incompatibilities or large stiffness. The
interfacial width at very high incompatibilities is smaller than the prediction
of the Gaussian chain model, and decreases upon increasing the statistical
segment length of the semi-flexible component.Comment: to appear in J.Chem.Phy
Simulations of the Magneto-rotational Instability in Core-Collapse Supernovae
We assess the importance of the magneto-rotational instability in
core-collapse supernovae by an analysis of the growth rates of unstable modes
in typical post-collapse systems and by numerical simulations of simplified
models. The interplay of differential rotation and thermal stratification
defines different instability regimes which we confirm in our simulations. We
investigate the termination of the growth of the MRI by parasitic
instabilities, establish scaling laws characterising the termination amplitude,
and study the long-term evolution of the saturated turbulent state.Comment: 6 pages, 1 figure. To appear in Proceedings of 4th International
Conference on Numerical Modeling of Space Plasma Flows (Chamonix 2009
Signaling Without Common Prior: An Experiment
The common prior assumption is pervasive in game-theoretic models with incomplete information. This paper investigates experimentally the importance of inducing a common prior in a two-person signaling game. For a specific probability distribution of the sender’s type, the long-run behavior without an induced common prior is shown to be different from the behavior when a common prior is induced, while for other distributions behavior is similar under both regimes. We also present a learning model that allows players to learn about the other players’ strategies and the prior distribution of the sender’s type. We show that this learning model accurately accounts for all main features of the data.common prior;signaling;experiment;learning
Lattice study of the infrared behavior of QCD Green's functions in Landau gauge
We summarize the current status of our numerical results for the gluon and
ghost propagators and for the Kugo-Ojima confinement parameter in quenched
SU(3) lattice Landau gauge theory. The data for the propagators are compared to
our results obtained in the case of full QCD, simulated using two flavors of
dynamical clover-improved Wilson fermions. We demonstrate that the infrared
behavior of the ghost propagator is consistent with the Kugo-Ojima confinement
criterion. Explicit violation of reflection positivity by the gluon propagator
is shown. Additionally, we present results of a running coupling constant both
at low and at large momenta.Comment: 7 pages, 8 figures, talk presented at Lattice2006 (Confinement and
Topology
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