3,003 research outputs found
Change point detection in social networksCritical review with experiments
© 2018 Elsevier Inc. Change point detection in social networks is an important element in developing the understanding of dynamic systems. This complex and growing area of research has no clear guidelines on what methods to use or in which circumstances. This paper critically discusses several possible network metrics to be used for a change point detection problem and conducts an experimental, comparative analysis using the Enron and MIT networks. Bayesian change point detection analysis is conducted on different global graph metrics (Size, Density, Average Clustering Coefficient, Average Shortest Path) as well as metrics derived from the Hierarchical and Block models (Entropy, Edge Probability, No. of Communities, Hierarchy Level Membership). The results produced the posterior probability of a change point at weekly time intervals that were analysed against ground truth change points using precision and recall measures. Results suggest that computationally heavy generative models offer only slightly better results compared to some of the global graph metrics. The simplest metrics used in the experiments, i.e. nodes and links numbers, are the recommended choice for detecting overall structural changes
Fast track children's hearing pilot: final report of the evaluation of the pilot
This report presents key findings of the evaluation of the Fast Track children’s hearings pilot in Scotland1. The research was undertaken by staff at the Universities of Glasgow, Stirling and Strathclyde between February 2003 and January 2005
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Development of predictive simulation capability for reactive multiphase flow
This is the final report of a Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of the project was to develop a self-sustained research program for advanced computer simulation of industrial reactive multiphase flows. The prototype research problem was a three-phase alumina precipitator used in the Bayer process, a key step in aluminum refining. Accomplishments included the development of an improved reaction mechanism of the alumina precipitation growth process, the development of an efficient methods for handling particle size distribution in multiphase flow simulation codes, the incorporation of precipitation growth and agglomeration kinetics in LANL's CFDLIB multiphase flow code library and the evaluation of multiphase turbulence closure models for bubbly flow simulations
Measurements of the magnetic field induced by a turbulent flow of liquid metal
Initial results from the Madison Dynamo Experiment provide details of the
inductive response of a turbulent flow of liquid sodium to an applied magnetic
field. The magnetic field structure is reconstructed from both internal and
external measurements. A mean toroidal magnetic field is induced by the flow
when an axial field is applied, thereby demonstrating the omega effect.
Poloidal magnetic flux is expelled from the fluid by the poloidal flow.
Small-scale magnetic field structures are generated by turbulence in the flow.
The resulting magnetic power spectrum exhibits a power-law scaling consistent
with the equipartition of the magnetic field with a turbulent velocity field.
The magnetic power spectrum has an apparent knee at the resistive dissipation
scale. Large-scale eddies in the flow cause significant changes to the
instantaneous flow profile resulting in intermittent bursts of non-axisymmetric
magnetic fields, demonstrating that the transition to a dynamo is not smooth
for a turbulent flow.Comment: 9 pages, 11 figures, invited talk by C. B. Forest at 2005 APS DPP
meeting, resubmitted to Physics of Plasma
Observation of a Turbulence-Induced Large Scale Magnetic Field
An axisymmetric magnetic field is applied to a spherical, turbulent flow of
liquid sodium. An induced magnetic dipole moment is measured which cannot be
generated by the interaction of the axisymmetric mean flow with the applied
field, indicating the presence of a turbulent electromotive force. It is shown
that the induced dipole moment should vanish for any axisymmetric laminar flow.
Also observed is the production of toroidal magnetic field from applied
poloidal magnetic field (the omega-effect). Its potential role in the
production of the induced dipole is discussed.Comment: 5 pages, 4 figures Revisions to accomodate peer-reviewer concerns;
changes to main text including simplification of a proof, Fig. 2 updated, and
minor typos and clarifications; Added refrences. Resubmitted to Phys. Rev.
Let
Intermittent magnetic field excitation by a turbulent flow of liquid sodium
The magnetic field measured in the Madison Dynamo Experiment shows
intermittent periods of growth when an axial magnetic field is applied. The
geometry of the intermittent field is consistent with the fastest growing
magnetic eigenmode predicted by kinematic dynamo theory using a laminar model
of the mean flow. Though the eigenmodes of the mean flow are decaying, it is
postulated that turbulent fluctuations of the velocity field change the flow
geometry such that the eigenmode growth rate is temporarily positive.
Therefore, it is expected that a characteristic of the onset of a turbulent
dynamo is magnetic intermittency.Comment: 5 pages, 7 figure
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