7,196 research outputs found
Recent Developments of World-Line Monte Carlo Methods
World-line quantum Monte Carlo methods are reviewed with an emphasis on
breakthroughs made in recent years. In particular, three algorithms -- the loop
algorithm, the worm algorithm, and the directed-loop algorithm -- for updating
world-line configurations are presented in a unified perspective. Detailed
descriptions of the algorithms in specific cases are also given.Comment: To appear in Journal of Physical Society of Japa
Schwinger-Dyson equations in large-N quantum field theories and nonlinear random processes
We propose a stochastic method for solving Schwinger-Dyson equations in
large-N quantum field theories. Expectation values of single-trace operators
are sampled by stationary probability distributions of the so-called nonlinear
random processes. The set of all histories of such processes corresponds to the
set of all planar diagrams in the perturbative expansions of the expectation
values of singlet operators. We illustrate the method on the examples of the
matrix-valued scalar field theory and the Weingarten model of random planar
surfaces on the lattice. For theories with compact field variables, such as
sigma-models or non-Abelian lattice gauge theories, the method does not
converge in the physically most interesting weak-coupling limit. In this case
one can absorb the divergences into a self-consistent redefinition of expansion
parameters. Stochastic solution of the self-consistency conditions can be
implemented as a "memory" of the random process, so that some parameters of the
process are estimated from its previous history. We illustrate this idea on the
example of two-dimensional O(N) sigma-model. Extension to non-Abelian lattice
gauge theories is discussed.Comment: 16 pages RevTeX, 14 figures; v2: Algorithm for the Weingarten model
corrected; v3: published versio
Fidelity susceptibility made simple: A unified quantum Monte Carlo approach
The fidelity susceptibility is a general purpose probe of phase transitions.
With its origin in quantum information and in the differential geometry
perspective of quantum states, the fidelity susceptibility can indicate the
presence of a phase transition without prior knowledge of the local order
parameter, as well as reveal the universal properties of a critical point. The
wide applicability of the fidelity susceptibility to quantum many-body systems
is, however, hindered by the limited computational tools to evaluate it. We
present a generic, efficient, and elegant approach to compute the fidelity
susceptibility of correlated fermions, bosons, and quantum spin systems in a
broad range of quantum Monte Carlo methods. It can be applied both to the
ground-state and non-zero temperature cases. The Monte Carlo estimator has a
simple yet universal form, which can be efficiently evaluated in simulations.
We demonstrate the power of this approach with applications to the Bose-Hubbard
model, the spin- XXZ model, and use it to examine the hypothetical
intermediate spin-liquid phase in the Hubbard model on the honeycomb lattice.Comment: new physical insight added in Sec. VI., improved data in Fig.
Modeling the ballistic-to-diffusive transition in nematode motility reveals variation in exploratory behavior across species
A quantitative understanding of organism-level behavior requires predictive
models that can capture the richness of behavioral phenotypes, yet are simple
enough to connect with underlying mechanistic processes. Here we investigate
the motile behavior of nematodes at the level of their translational motion on
surfaces driven by undulatory propulsion. We broadly sample the nematode
behavioral repertoire by measuring motile trajectories of the canonical lab
strain N2 as well as wild strains and distant species. We focus on
trajectory dynamics over timescales spanning the transition from ballistic
(straight) to diffusive (random) movement and find that salient features of the
motility statistics are captured by a random walk model with independent
dynamics in the speed, bearing and reversal events. We show that the model
parameters vary among species in a correlated, low-dimensional manner
suggestive of a common mode of behavioral control and a trade-off between
exploration and exploitation. The distribution of phenotypes along this primary
mode of variation reveals that not only the mean but also the variance varies
considerably across strains, suggesting that these nematode lineages employ
contrasting ``bet-hedging'' strategies for foraging.Comment: 46 pages, 18 figures, 6 table
Genome-wide analysis of ivermectin response by Onchocerca volvulus reveals that genetic drift and soft selective sweeps contribute to loss of drug sensitivity
Treatment of onchocerciasis using mass ivermectin administration has reduced morbidity and transmission throughout Africa and Central/South America. Mass drug administration is likely to exert selection pressure on parasites, and phenotypic and genetic changes in several Onchocerca volvulus populations from Cameroon and Ghana-exposed to more than a decade of regular ivermectin treatment-have raised concern that sub-optimal responses to ivermectin's anti-fecundity effect are becoming more frequent and may spread.Pooled next generation sequencing (Pool-seq) was used to characterise genetic diversity within and between 108 adult female worms differing in ivermectin treatment history and response. Genome-wide analyses revealed genetic variation that significantly differentiated good responder (GR) and sub-optimal responder (SOR) parasites. These variants were not randomly distributed but clustered in ~31 quantitative trait loci (QTLs), with little overlap in putative QTL position and gene content between the two countries. Published candidate ivermectin SOR genes were largely absent in these regions; QTLs differentiating GR and SOR worms were enriched for genes in molecular pathways associated with neurotransmission, development, and stress responses. Finally, single worm genotyping demonstrated that geographic isolation and genetic change over time (in the presence of drug exposure) had a significantly greater role in shaping genetic diversity than the evolution of SOR.This study is one of the first genome-wide association analyses in a parasitic nematode, and provides insight into the genomics of ivermectin response and population structure of O. volvulus. We argue that ivermectin response is a polygenically-determined quantitative trait (QT) whereby identical or related molecular pathways but not necessarily individual genes are likely to determine the extent of ivermectin response in different parasite populations. Furthermore, we propose that genetic drift rather than genetic selection of SOR is the underlying driver of population differentiation, which has significant implications for the emergence and potential spread of SOR within and between these parasite populations
On-the-fly Fast Mean-Field Model-Checking: Extended Version
A novel, scalable, on-the-fly model-checking procedure is presented to verify
bounded PCTL properties of selected individuals in the context of very large
systems of independent interacting objects. The proposed procedure combines
on-the-fly model checking techniques with deterministic mean-field
approximation in discrete time. The asymptotic correctness of the procedure is
shown and some results of the application of a prototype implementation of the
FlyFast model-checker are presented
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