8,972 research outputs found
Structure of large random hypergraphs
The theme of this paper is the derivation of analytic formulae for certain
large combinatorial structures. The formulae are obtained via fluid limits of
pure jump type Markov processes, established under simple conditions on the
Laplace transforms of their Levy kernels. Furthermore, a related Gaussian
approximation allows us to describe the randomness which may persist in the
limit when certain parameters take critical values. Our method is quite
general, but is applied here to vertex identifiability in random hypergraphs. A
vertex v is identifiable in n steps if there is a hyperedge containing v all of
whose other vertices are identifiable in fewer than n steps. We say that a
hyperedge is identifiable if every one of its vertices is identifiable. Our
analytic formulae describe the asymptotics of the number of identifiable
vertices and the number of identifiable hyperedges for a Poisson random
hypergraph on a set of N vertices, in the limit as N goes to infinity.Comment: Revised version with minor conceptual improvements and additional
discussion. 32 pages, 5 figure
Differential equation approximations for Markov chains
We formulate some simple conditions under which a Markov chain may be
approximated by the solution to a differential equation, with quantifiable
error probabilities. The role of a choice of coordinate functions for the
Markov chain is emphasised. The general theory is illustrated in three
examples: the classical stochastic epidemic, a population process model with
fast and slow variables, and core-finding algorithms for large random
hypergraphs.Comment: Published in at http://dx.doi.org/10.1214/07-PS121 the Probability
Surveys (http://www.i-journals.org/ps/) by the Institute of Mathematical
Statistics (http://www.imstat.org
A high pressure, high temperature combustor and turbine-cooling test facility
A new test facility is being constructed for developing turbine-cooling and combustor technology for future generation aircraft gas turbine engines. Prototype engine hardware will be investigated in this new facility at gas stream conditions up to 2480 K average turbine inlet temperature and 4.14 x 10 to the 6th power n sq m turbine inlet pressure. The facility will have the unique feature of fully automated control and data acquisition through the use of an integrated system of mini-computers and programmable controllers which will result in more effective use of operating time, will limit the number of operators required, and will provide built in self protection safety systems. The facility and the planning and design considerations are described
Overlay copy technique to provide high-contrast electron micrographs for automatic metallographic analysis
Overlay copy technique to provide high-contrast electron micrographs for automatically determining quantitative microstructure of multiphase specimen
Employing pre-stress to generate finite cloaks for antiplane elastic waves
It is shown that nonlinear elastic pre-stress of neo-Hookean hyperelastic
materials can be used as a mechanism to generate finite cloaks and thus render
objects near-invisible to incoming antiplane elastic waves. This approach
appears to negate the requirement for special cloaking metamaterials with
inhomogeneous and anisotropic material properties in this case. These
properties are induced naturally by virtue of the pre-stress. This appears to
provide a mechanism for broadband cloaking since dispersive effects due to
metamaterial microstructure will not arise.Comment: 4 pages, 2 figure
Reducing the Manufacturing and Management Costs of Tractors and Agricultural Equipment
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is an Invited Paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 5 (2003): J. Reid, J. Schueller, and W. Norris. Reducing the Manufacturing and Management Costs of Tractors and Agricultural Equipment. Club of Bologna. Vol. V. December 2003
A wider audience: Turning VLBI into a survey instrument
Radio observations using the Very Long Baseline Interferometry (VLBI)
technique typically have fields of view of only a few arcseconds, due to the
computational problems inherent in imaging larger fields. Furthermore,
sensitivity limitations restrict observations to very compact and bright
objects, which are few and far between on the sky. Thus, while most branches of
observational astronomy can carry out sensitive, wide-field surveys, VLBI
observations are limited to targeted observations of carefully selected
objects. However, recent advances in technology have made it possible to carry
out the computations required to target hundreds of sources simultaneously.
Furthermore, sensitivity upgrades have dramatically increased the number of
objects accessible to VLBI observations. The combination of these two
developments have enhanced the survey capabilities of VLBI observations such
that it is now possible to observe (almost) any point in the sky with
milli-arcsecond resolution. In this talk I review the development of wide-field
VLBI, which has made significant progress over the last three years.Comment: Invited review at the General Assembly of the Astronomische
Gesellschaf
U.S. Coast Guard Boat Recovery Simulation at NASA Ames Vertical Motion Simulator
The Boat Recovery Simulation was a collaboration between the U.S. Coast Guard and NASA. The experiment was conducted at the NASA Ames Vertical Motion Simulator (VMS). The goals were to (1) design a VMS experiment that can accurately simulate the motion of high sea conditions and to (2) collect data for the U.S. Coast Guard on human performance related to small boat recovery operations. The experiment setup included a software operation model designed around empirical boat position data; a replica boat section manufactured to incorporate real-world task elements; and the means to collect objective and subjective data from human participants. The VMS provided a viable testbed to assess certified U.S. Coast Guard crewmembers task performance while in motion
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