6,516 research outputs found
Chaos in spin glasses revealed through thermal boundary conditions
We study the fragility of spin glasses to small temperature perturbations
numerically using population annealing Monte Carlo. We apply thermal boundary
conditions to a three-dimensional Edwards-Anderson Ising spin glass. In thermal
boundary conditions all eight combinations of periodic versus antiperiodic
boundary conditions in the three spatial directions are present, each appearing
in the ensemble with its respective statistical weight determined by its free
energy. We show that temperature chaos is revealed in the statistics of
crossings in the free energy for different boundary conditions. By studying the
energy difference between boundary conditions at free-energy crossings, we
determine the domain-wall fractal dimension. Similarly, by studying the number
of crossings, we determine the chaos exponent. Our results also show that
computational hardness in spin glasses and the presence of chaos are closely
related.Comment: 4 pages, 4 figure
Dynamic Implicit-Solvent Coarse-Grained Models of Lipid Bilayer Membranes : Fluctuating Hydrodynamics Thermostat
Many coarse-grained models have been developed for equilibrium studies of
lipid bilayer membranes. To achieve in simulations access to length-scales and
time-scales difficult to attain in fully atomistic molecular dynamics, these
coarse-grained models provide a reduced description of the molecular degrees of
freedom and often remove entirely representation of the solvent degrees of
freedom. In such implicit-solvent models the solvent contributions are treated
through effective interaction terms within an effective potential for the free
energy. For investigations of kinetics, Langevin dynamics is often used.
However, for many dynamical processes within bilayers this approach is
insufficient since it neglects important correlations and dynamical
contributions that are missing as a result of the momentum transfer that would
have occurred through the solvent. To address this issue, we introduce a new
thermostat based on fluctuating hydrodynamics for dynamic simulations of
implicit-solvent coarse-grained models. Our approach couples the coarse-grained
degrees of freedom to a stochastic continuum field that accounts for both the
solvent hydrodynamics and thermal fluctuations. We show our approach captures
important correlations in the dynamics of lipid bilayers that are missing in
simulations performed using conventional Langevin dynamics. For both planar
bilayer sheets and bilayer vesicles, we investigate the diffusivity of lipids,
spatial correlations, and lipid flow within the bilayer. The presented
fluctuating hydrodynamics approaches provide a promising way to extend
implicit-solvent coarse-grained lipid models for use in studies of dynamical
processes within bilayers
Supervised Hypergraph Reconstruction
We study an issue commonly seen with graph data analysis: many real-world
complex systems involving high-order interactions are best encoded by
hypergraphs; however, their datasets often end up being published or studied
only in the form of their projections (with dyadic edges). To understand this
issue, we first establish a theoretical framework to characterize this issue's
implications and worst-case scenarios. The analysis motivates our formulation
of the new task, supervised hypergraph reconstruction: reconstructing a
real-world hypergraph from its projected graph, with the help of some existing
knowledge of the application domain.
To reconstruct hypergraph data, we start by analyzing hyperedge distributions
in the projection, based on which we create a framework containing two modules:
(1) to handle the enormous search space of potential hyperedges, we design a
sampling strategy with efficacy guarantees that significantly narrows the space
to a smaller set of candidates; (2) to identify hyperedges from the candidates,
we further design a hyperedge classifier in two well-working variants that
capture structural features in the projection. Extensive experiments validate
our claims, approach, and extensions. Remarkably, our approach outperforms all
baselines by an order of magnitude in accuracy on hard datasets. Our code and
data can be downloaded from bit.ly/SHyRe
Collaborative Innovation and Economic Growth: A Comment on China’s Innovation Policies
China has also taken steps to encourage the creation of intellectual property by Chinese companies. This Article will first examine the nature of those policies, then consider their impact on the goal of better innovation in China, as well as the impact on multi-national companies that wish to do business in China. The Article will conclude with suggestions about the best ways to build innovation policy to encourage sustainable relationships between China and multi-national companies
- …