30,223 research outputs found
Labeling Workflow Views with Fine-Grained Dependencies
This paper considers the problem of efficiently answering reachability
queries over views of provenance graphs, derived from executions of workflows
that may include recursion. Such views include composite modules and model
fine-grained dependencies between module inputs and outputs. A novel
view-adaptive dynamic labeling scheme is developed for efficient query
evaluation, in which view specifications are labeled statically (i.e. as they
are created) and data items are labeled dynamically as they are produced during
a workflow execution. Although the combination of fine-grained dependencies and
recursive workflows entail, in general, long (linear-size) data labels, we show
that for a large natural class of workflows and views, labels are compact
(logarithmic-size) and reachability queries can be evaluated in constant time.
Experimental results demonstrate the benefit of this approach over the
state-of-the-art technique when applied for labeling multiple views.Comment: VLDB201
Modified optimal control pilot model for computer-aided design and analysis
This paper presents the theoretical development of a modified optimal control pilot model based upon the optimal control model (OCM) of the human operator developed by Kleinman, Baron, and Levison. This model is input compatible with the OCM and retains other key aspects of the OCM, such as a linear quadratic solution for the pilot gains with inclusion of control rate in the cost function, a Kalman estimator, and the ability to account for attention allocation and perception threshold effects. An algorithm designed for each implementation in current dynamic systems analysis and design software is presented. Example results based upon the analysis of a tracking task using three basic dynamic systems are compared with measured results and with similar analyses performed with the OCM and two previously proposed simplified optimal pilot models. The pilot frequency responses and error statistics obtained with this modified optimal control model are shown to compare more favorably to the measured experimental results than the other previously proposed simplified models evaluated
Search and Result Presentation in Scientific Workflow Repositories
We study the problem of searching a repository of complex hierarchical
workflows whose component modules, both composite and atomic, have been
annotated with keywords. Since keyword search does not use the graph structure
of a workflow, we develop a model of workflows using context-free bag grammars.
We then give efficient polynomial-time algorithms that, given a workflow and a
keyword query, determine whether some execution of the workflow matches the
query. Based on these algorithms we develop a search and ranking solution that
efficiently retrieves the top-k grammars from a repository. Finally, we propose
a novel result presentation method for grammars matching a keyword query, based
on representative parse-trees. The effectiveness of our approach is validated
through an extensive experimental evaluation
Unified Brane Gravity: Cosmological Dark Matter from Scale Dependent Newton Constant
We analyze, within the framework of unified brane gravity, the weak-field
perturbations caused by the presence of matter on a 3-brane. Although deviating
from the Randall-Sundrum approach, the masslessness of the graviton is still
preserved. In particular, the four-dimensional Newton force law is recovered,
but serendipitously, the corresponding Newton constant is shown to be
necessarily lower than the one which governs FRW cosmology. This has the
potential to puzzle out cosmological dark matter. A subsequent conjecture
concerning galactic dark matter follows.Comment: 6 pages, to be published in Phys. Rev.
Answering Regular Path Queries on Workflow Provenance
This paper proposes a novel approach for efficiently evaluating regular path
queries over provenance graphs of workflows that may include recursion. The
approach assumes that an execution g of a workflow G is labeled with
query-agnostic reachability labels using an existing technique. At query time,
given g, G and a regular path query R, the approach decomposes R into a set of
subqueries R1, ..., Rk that are safe for G. For each safe subquery Ri, G is
rewritten so that, using the reachability labels of nodes in g, whether or not
there is a path which matches Ri between two nodes can be decided in constant
time. The results of each safe subquery are then composed, possibly with some
small unsafe remainder, to produce an answer to R. The approach results in an
algorithm that significantly reduces the number of subqueries k over existing
techniques by increasing their size and complexity, and that evaluates each
subquery in time bounded by its input and output size. Experimental results
demonstrate the benefit of this approach
Provenance Views for Module Privacy
Scientific workflow systems increasingly store provenance information about
the module executions used to produce a data item, as well as the parameter
settings and intermediate data items passed between module executions. However,
authors/owners of workflows may wish to keep some of this information
confidential. In particular, a module may be proprietary, and users should not
be able to infer its behavior by seeing mappings between all data inputs and
outputs. The problem we address in this paper is the following: Given a
workflow, abstractly modeled by a relation R, a privacy requirement \Gamma and
costs associated with data. The owner of the workflow decides which data
(attributes) to hide, and provides the user with a view R' which is the
projection of R over attributes which have not been hidden. The goal is to
minimize the cost of hidden data while guaranteeing that individual modules are
\Gamma -private. We call this the "secureview" problem. We formally define the
problem, study its complexity, and offer algorithmic solutions
An investigation of the optimal conditions of rocket motion in the vicinity of a planet
Optimal control of points of motion for mass transfer in vacuums in gravitational fiel
Clash of symmetries on the brane
If our 3+1-dimensional universe is a brane or domain wall embedded in a
higher dimensional space, then a phenomenon we term the ``clash of symmetries''
provides a new method of breaking some continuous symmetries. A global
symmetry is spontaneously broken
to , where the continuous subgroup
can be embedded in several different ways in the parent group
, and . A certain
class of topological domain wall solutions connect two vacua that are invariant
under {\it differently embedded} subgroups. There is then
enhanced symmetry breakdown to the intersection of these two subgroups on the
domain wall. This is the ``clash''. In the brane limit, we obtain a
configuration with symmetries in the bulk but the smaller
intersection symmetry on the brane itself. We illustrate this idea using a
permutation symmetric three-Higgs-triplet toy model exploiting the distinct
, and spin U(2) subgroups of U(3). The three disconnected portions
of the vacuum manifold can be treated symmetrically through the construction of
a three-fold planar domain wall junction configuration, with our universe at
the nexus. A possible connection with is discussed.Comment: 30 pages, 9 embedded figure
A simulation study of the flight dynamics of elastic aircraft. Volume 1: Experiment, results and analysis
The simulation experiment described addresses the effects of structural flexibility on the dynamic characteristics of a generic family of aircraft. The simulation was performed using the NASA Langley VMS simulation facility. The vehicle models were obtained as part of this research. The simulation results include complete response data and subjective pilot ratings and comments and so allow a variety of analyses. The subjective ratings and analysis of the time histories indicate that increased flexibility can lead to increased tracking errors, degraded handling qualities, and changes in the frequency content of the pilot inputs. These results, furthermore, are significantly affected by the visual cues available to the pilot
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