83,120 research outputs found
Symmetry-Based Search Space Reduction For Grid Maps
In this paper we explore a symmetry-based search space reduction technique
which can speed up optimal pathfinding on undirected uniform-cost grid maps by
up to 38 times. Our technique decomposes grid maps into a set of empty
rectangles, removing from each rectangle all interior nodes and possibly some
from along the perimeter. We then add a series of macro-edges between selected
pairs of remaining perimeter nodes to facilitate provably optimal traversal
through each rectangle. We also develop a novel online pruning technique to
further speed up search. Our algorithm is fast, memory efficient and retains
the same optimality and completeness guarantees as searching on an unmodified
grid map
Discontinuous Molecular Dynamics for Semi-Flexible and Rigid Bodies
A general framework for performing event-driven simulations of systems with
semi-flexible or rigid bodies interacting under impulsive torques and forces is
outlined. Two different approaches are presented. In the first, the dynamics
and interaction rules are derived from Lagrangian mechanics in the presence of
constraints. This approach is most suitable when the body is composed of
relatively few point masses or is semi-flexible. In the second method, the
equations of rigid bodies are used to derive explicit analytical expressions
for the free evolution of arbitrary rigid molecules and to construct a simple
scheme for computing interaction rules. Efficient algorithms for the search for
the times of interaction events are designed in this context, and the handling
of missed interaction events is discussed.Comment: 16 pages, double column revte
GPU LSM: A Dynamic Dictionary Data Structure for the GPU
We develop a dynamic dictionary data structure for the GPU, supporting fast
insertions and deletions, based on the Log Structured Merge tree (LSM). Our
implementation on an NVIDIA K40c GPU has an average update (insertion or
deletion) rate of 225 M elements/s, 13.5x faster than merging items into a
sorted array. The GPU LSM supports the retrieval operations of lookup, count,
and range query operations with an average rate of 75 M, 32 M and 23 M
queries/s respectively. The trade-off for the dynamic updates is that the
sorted array is almost twice as fast on retrievals. We believe that our GPU LSM
is the first dynamic general-purpose dictionary data structure for the GPU.Comment: 11 pages, accepted to appear on the Proceedings of IEEE International
Parallel and Distributed Processing Symposium (IPDPS'18
A neural network for mining large volumes of time series data
Efficiently mining large volumes of time series data is amongst the most challenging problems that are fundamental in many fields such as industrial process monitoring, medical data analysis and business forecasting. This paper discusses a high-performance neural network for mining large time series data set and some practical issues on time series data mining. Examples of how this technology is used to search the engine data within a major UK eScience Grid project (DAME) for supporting the maintenance of Rolls-Royce aero-engine are presented
Robust semicoherent searches for continuous gravitational waves with noise and signal models including hours to days long transients
The vulnerability to single-detector instrumental artifacts in standard
detection methods for long-duration quasimonochromatic gravitational waves from
nonaxisymmetric rotating neutron stars [continuous waves (CWs)] was addressed
in past work [D. Keitel et al., Phys. Rev. D 89, 064023 (2014).] by a Bayesian
approach. An explicit model of persistent single-detector disturbances led to a
generalized detection statistic with improved robustness against such
artifacts. Since many strong outliers in semicoherent searches of LIGO data are
caused by transient disturbances that last only a few hours, we extend the
noise model to cover such limited-duration disturbances, and demonstrate
increased robustness in realistic simulated data. Besides long-duration CWs,
neutron stars could also emit transient signals which, for a limited time, also
follow the CW signal model (tCWs). As a pragmatic alternative to specialized
transient searches, we demonstrate how to make standard semicoherent CW
searches more sensitive to transient signals. Considering tCWs in a single
segment of a semicoherent search, Bayesian model selection yields a new
detection statistic that does not add significant computational cost. On
simulated data, we find that it increases sensitivity towards tCWs, even of
varying durations, while not sacrificing sensitivity to classical CW signals,
and still being robust to transient or persistent single-detector instrumental
artifacts.Comment: 16 pages, 6 figures, REVTeX4.
A Formal Framework for Linguistic Annotation
`Linguistic annotation' covers any descriptive or analytic notations applied
to raw language data. The basic data may be in the form of time functions --
audio, video and/or physiological recordings -- or it may be textual. The added
notations may include transcriptions of all sorts (from phonetic features to
discourse structures), part-of-speech and sense tagging, syntactic analysis,
`named entity' identification, co-reference annotation, and so on. While there
are several ongoing efforts to provide formats and tools for such annotations
and to publish annotated linguistic databases, the lack of widely accepted
standards is becoming a critical problem. Proposed standards, to the extent
they exist, have focussed on file formats. This paper focuses instead on the
logical structure of linguistic annotations. We survey a wide variety of
existing annotation formats and demonstrate a common conceptual core, the
annotation graph. This provides a formal framework for constructing,
maintaining and searching linguistic annotations, while remaining consistent
with many alternative data structures and file formats.Comment: 49 page
- …