536 research outputs found
Stress concentrations around voids in three dimensions : The roots of failure
Funding This work forms part of a NERC New Investigator award for DH (NE/I001743/1), which is gratefully acknowledged. Acknowledgments The authors would like to acknowledge the reviewers, Elizabeth Ritz and Phillip Resor. Their reviews were very constructive, both helping to improve the manuscripts consistency and highlighting a number of errors in the initial submission. The authors would also like to thank Lydia Jagger's keen eye and patience, she helped greatly in removing a number of grammatical errors from the initial draft.Peer reviewedPublisher PD
Pore geometry as a control on rock strength
This study was funded via RJW's University of Leicester start-up fund, as part of AAB's PhD project. We thank Don Swanson and Mike Poland at HVO, Hawai'i, for their help and advice during fieldwork planning and sample collection in the Koa'e fault system, and the National Park Service for granting a research permit to collect rock samples. Sergio Vinciguerra is thanked for access to the Rock Mechanics and Physics lab at the British Geological Survey and Audrey Ougier-Simonin is thanked for her help preparing samples and advice during testing. We thank Mike Heap (EOST Strasbourg) and an anonymous reviewer for their detailed and careful comments that greatly improved the manuscript.Peer reviewedPostprin
k-server via multiscale entropic regularization
We present an -competitive randomized algorithm for the
-server problem on hierarchically separated trees (HSTs). This is the first
-competitive randomized algorithm for which the competitive ratio is
independent of the size of the underlying HST. Our algorithm is designed in the
framework of online mirror descent where the mirror map is a multiscale
entropy. When combined with Bartal's static HST embedding reduction, this leads
to an -competitive algorithm on any -point metric
space. We give a new dynamic HST embedding that yields an -competitive algorithm on any metric space where the ratio of the
largest to smallest non-zero distance is at most
The finite mass mesh method
The finite mass method is a purely Lagrangian scheme for the spatial discretisation of the macroscopic phenomenological laws that govern the flow of compressible fluids. In this article we investigate how to take into account long range gravitational forces in the framework of the finite mass method. This is achieved by incorporating an extra discrete potential energy of the gravitational field into the Lagrangian that underlies the finite mass method. The discretisation of the potential is done in an Eulerian fashion and employs an adaptive tensor product mesh fixed in space, hence the name finite mass mesh method for the new scheme. The transfer of information between the mass packets of the finite mass method and the discrete potential equation relies on numerical quadrature, for which different strategies will be proposed. The performance of the extended finite mass method for the simulation of two-dimensional gas pillars under self-gravity will be reporte
Single File Diffusion enhancement in a fluctuating modulated 1D channel
We show that the diffusion of a single file of particles moving in a
fluctuating modulated 1D channel is enhanced with respect to the one in a bald
pipe. This effect, induced by the fluctuations of the modulation, is favored by
the incommensurability between the channel potential modulation and the moving
file periodicity. This phenomenon could be of importance in order to optimize
the critical current in superconductors, in particular in the case where mobile
vortices move in 1D channels designed by adapted patterns of pinning sites.Comment: 4 pages, 4 figure
Bayesian Best-Arm Identification for Selecting Influenza Mitigation Strategies
Pandemic influenza has the epidemic potential to kill millions of people.
While various preventive measures exist (i.a., vaccination and school
closures), deciding on strategies that lead to their most effective and
efficient use remains challenging. To this end, individual-based
epidemiological models are essential to assist decision makers in determining
the best strategy to curb epidemic spread. However, individual-based models are
computationally intensive and it is therefore pivotal to identify the optimal
strategy using a minimal amount of model evaluations. Additionally, as
epidemiological modeling experiments need to be planned, a computational budget
needs to be specified a priori. Consequently, we present a new sampling
technique to optimize the evaluation of preventive strategies using fixed
budget best-arm identification algorithms. We use epidemiological modeling
theory to derive knowledge about the reward distribution which we exploit using
Bayesian best-arm identification algorithms (i.e., Top-two Thompson sampling
and BayesGap). We evaluate these algorithms in a realistic experimental setting
and demonstrate that it is possible to identify the optimal strategy using only
a limited number of model evaluations, i.e., 2-to-3 times faster compared to
the uniform sampling method, the predominant technique used for epidemiological
decision making in the literature. Finally, we contribute and evaluate a
statistic for Top-two Thompson sampling to inform the decision makers about the
confidence of an arm recommendation
Discovering Valuable Items from Massive Data
Suppose there is a large collection of items, each with an associated cost
and an inherent utility that is revealed only once we commit to selecting it.
Given a budget on the cumulative cost of the selected items, how can we pick a
subset of maximal value? This task generalizes several important problems such
as multi-arm bandits, active search and the knapsack problem. We present an
algorithm, GP-Select, which utilizes prior knowledge about similarity be- tween
items, expressed as a kernel function. GP-Select uses Gaussian process
prediction to balance exploration (estimating the unknown value of items) and
exploitation (selecting items of high value). We extend GP-Select to be able to
discover sets that simultaneously have high utility and are diverse. Our
preference for diversity can be specified as an arbitrary monotone submodular
function that quantifies the diminishing returns obtained when selecting
similar items. Furthermore, we exploit the structure of the model updates to
achieve an order of magnitude (up to 40X) speedup in our experiments without
resorting to approximations. We provide strong guarantees on the performance of
GP-Select and apply it to three real-world case studies of industrial
relevance: (1) Refreshing a repository of prices in a Global Distribution
System for the travel industry, (2) Identifying diverse, binding-affine
peptides in a vaccine de- sign task and (3) Maximizing clicks in a web-scale
recommender system by recommending items to users
Structure and Melting of Two-Species Charged Clusters in a Parabolic Trap
We consider a system of charged particles interacting with an unscreened
Coulomb repulsion in a two-dimensional parabolic confining trap. The static
charge on a portion of the particles is twice as large as the charge on the
remaining particles. The particles separate into a shell structure with those
of greater charge situated farther from the center of the trap. As we vary the
ratio of the number of particles of the two species, we find that for certain
configurations, the symmetry of the arrangement of the inner cluster of
singly-charged particles matches the symmetry of the outer ring of
doubly-charged particles. These matching configurations have a higher melting
temperature and a higher thermal threshold for intershell rotation between the
species than the nonmatching configurations.Comment: 4 pages, 6 postscript figure
Yield conditions for deformation of amorphous polymer glasses
Shear yielding of glassy polymers is usually described in terms of the
pressure-dependent Tresca or von Mises yield criteria. We test these criteria
against molecular dynamics simulations of deformation in amorphous polymer
glasses under triaxial loading conditions that are difficult to realize in
experiments. Difficulties and ambiguities in extending several standard
definitions of the yield point to triaxial loads are described. Two
definitions, the maximum and offset octahedral stresses, are then used to
evaluate the yield stress for a wide range of model parameters. In all cases,
the onset of shear is consistent with the pressure-modified von Mises
criterion, and the pressure coefficient is nearly independent of many
parameters. Under triaxial tensile loading, the mode of failure changes to
cavitation.Comment: 9 pages, 8 figures, revte
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