9,504 research outputs found
Dissimilar bouncy walkers
We consider the dynamics of a one-dimensional system consisting of dissimilar
hardcore interacting (bouncy) random walkers. The walkers' (diffusing
particles') friction constants xi_n, where n labels different bouncy walkers,
are drawn from a distribution rho(xi_n). We provide an approximate analytic
solution to this recent single-file problem by combining harmonization and
effective medium techniques. Two classes of systems are identified: when
rho(xi_n) is heavy-tailed, rho(xi_n)=A xi_n^(-1-\alpha) (0<alpha<1) for large
xi_n, we identify a new universality class in which density relaxations,
characterized by the dynamic structure factor S(Q,t), follows a Mittag-Leffler
relaxation, and the the mean square displacement of a tracer particle (MSD)
grows as t^delta with time t, where delta=alpha/(1+\alpha). If instead rho is
light-tailedsuch that the mean friction constant exist, S(Q,t) decays
exponentially and the MSD scales as t^(1/2). We also derive tracer particle
force response relations. All results are corroborated by simulations and
explained in a simplified model.Comment: 11 pages, to appear in Journal of Chemical Physic
Optimal target search on a fast folding polymer chain with volume exchange
We study the search process of a target on a rapidly folding polymer (`DNA')
by an ensemble of particles (`proteins'), whose search combines 1D diffusion
along the chain, Levy type diffusion mediated by chain looping, and volume
exchange. A rich behavior of the search process is obtained with respect to the
physical parameters, in particular, for the optimal search.Comment: 4 pages, 3 figures, REVTe
Optimizing evacuation flow in a two-channel exclusion process
We use a basic setup of two coupled exclusion processes to model a stylised
situation in evacuation dynamics, in which evacuees have to choose between two
escape routes. The coupling between the two processes occurs through one common
point at which particles are injected, the process can be controlled by
directing incoming individuals into either of the two escape routes. Based on a
mean-field approach we determine the phase behaviour of the model, and
analytically compute optimal control strategies, maximising the total current
through the system. Results are confirmed by numerical simulations. We also
show that dynamic intervention, exploiting fluctuations about the mean-field
stationary state, can lead to a further increase in total current.Comment: 16 pages, 6 figure
Turbulence transition and the edge of chaos in pipe flow
The linear stability of pipe flow implies that only perturbations of
sufficient strength will trigger the transition to turbulence. In order to
determine this threshold in perturbation amplitude we study the \emph{edge of
chaos} which separates perturbations that decay towards the laminar profile and
perturbations that trigger turbulence. Using the lifetime as an indicator and
methods developed in (Skufca et al, Phys. Rev. Lett. {\bf 96}, 174101 (2006))
we show that superimposed on an overall -scaling predicted and studied
previously there are small, non-monotonic variations reflecting folds in the
edge of chaos. By tracing the motion in the edge we find that it is formed by
the stable manifold of a unique flow field that is dominated by a pair of
downstream vortices, asymmetrically placed towards the wall. The flow field
that generates the edge of chaos shows intrinsic chaotic dynamics.Comment: 4 pages, 5 figure
Catastrophic vs Gradual Collapse of Thin-Walled Nanocrystalline Ni Hollow Cylinders As Building Blocks of Microlattice Structures
Lightweight yet stiff and strong lattice structures are attractive for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. Recent breakthroughs in manufacturing enable efficient fabrication of hierarchically architected microlattices, with dimensional control spanning seven orders of magnitude in length scale. These materials have the potential to exploit desirable nanoscale-size effects in a macroscopic structure, as long as their mechanical behavior at each appropriate scale – nano, micro, and macro levels – is properly understood. In this letter, we report the nanomechanical response of individual microlattice members. We show that hollow nanocrystalline Ni cylinders differing only in wall thicknesses, 500 and 150 nm, exhibit strikingly different collapse modes: the 500 nm sample collapses in a brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than predicted by shell buckling theory, likely due to localized buckling and fracture events observed during in situ compression experiments. We attribute this difference to the size-induced transition in deformation behavior, unique to nanoscale, and discuss it in the framework of “size effects” in crystalline strength
A Gas Giant Circumbinary Planet Transiting the F Star Primary of the Eclipsing Binary Star KIC 4862625 and the Independent Discovery and Characterization of the two transiting planets in the Kepler-47 System
We report the discovery of a transiting, gas giant circumbinary planet
orbiting the eclipsing binary KIC 4862625 and describe our independent
discovery of the two transiting planets orbiting Kepler-47 (Orosz et al. 2012).
We describe a simple and semi-automated procedure for identifying individual
transits in light curves and present our follow-up measurements of the two
circumbinary systems. For the KIC 4862625 system, the 0.52+/-0.018 RJup radius
planet revolves every ~138 days and occults the 1.47+/-0.08 MSun, 1.7 +/-0.06
RSun F8 IV primary star producing aperiodic transits of variable durations
commensurate with the configuration of the eclipsing binary star. Our best-fit
model indicates the orbit has a semi-major axis of 0.64 AU and is slightly
eccentric, e=0.1. For the Kepler-47 system, we confirm the results of Orosz et
al. (2012). Modulations in the radial velocity of KIC 4862625A are measured
both spectroscopically and photometrically, i.e. via Doppler boosting, and
produce similar results.Comment: 40 pages, 17 figure
Simulating adiabatic evolution of gapped spin systems
We show that adiabatic evolution of a low-dimensional lattice of quantum
spins with a spectral gap can be simulated efficiently. In particular, we show
that as long as the spectral gap \Delta E between the ground state and the
first excited state is any constant independent of n, the total number of
spins, then the ground-state expectation values of local operators, such as
correlation functions, can be computed using polynomial space and time
resources. Our results also imply that the local ground-state properties of any
two spin models in the same quantum phase can be efficiently obtained from each
other. A consequence of these results is that adiabatic quantum algorithms can
be simulated efficiently if the spectral gap doesn't scale with n. The
simulation method we describe takes place in the Heisenberg picture and does
not make use of the finitely correlated state/matrix product state formalism.Comment: 13 pages, 2 figures, minor change
General Monogamy Inequality for Bipartite Qubit Entanglement
We consider multipartite states of qubits and prove that their bipartite
quantum entanglement, as quantified by the concurrence, satisfies a monogamy
inequality conjectured by Coffman, Kundu, and Wootters. We relate this monogamy
inequality to the concept of frustration of correlations in quantum spin
systems.Comment: Fixed spelling mistake. Added references. Fixed error in
transformation law. Shorter and more explicit proof of capacity formula.
Reference added. Rewritten introduction and conclusion
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