38,840 research outputs found
On Conditional Statistics in Scalar Turbulence: Theory vs. Experiment
We consider turbulent advection of a scalar field T(\B.r), passive or
active, and focus on the statistics of gradient fields conditioned on scalar
differences across a scale . In particular we focus on two
conditional averages and
. We find exact relations between
these averages, and with the help of the fusion rules we propose a general
representation for these objects in terms of the probability density function
of . These results offer a new way to analyze
experimental data that is presented in this paper. The main question that we
ask is whether the conditional average is linear in . We show that there exists a dimensionless
parameter which governs the deviation from linearity. The data analysis
indicates that this parameter is very small for passive scalar advection, and
is generally a decreasing function of the Rayleigh number for the convection
data.Comment: Phys. Rev. E, Submitted. REVTeX, 10 pages, 5 figs. (not included) PS
Source of the paper with figure available at
http://lvov.weizmann.ac.il/onlinelist.html#unpub
Technical Report: Cooperative Multi-Target Localization With Noisy Sensors
This technical report is an extended version of the paper 'Cooperative
Multi-Target Localization With Noisy Sensors' accepted to the 2013 IEEE
International Conference on Robotics and Automation (ICRA).
This paper addresses the task of searching for an unknown number of static
targets within a known obstacle map using a team of mobile robots equipped with
noisy, limited field-of-view sensors. Such sensors may fail to detect a subset
of the visible targets or return false positive detections. These measurement
sets are used to localize the targets using the Probability Hypothesis Density,
or PHD, filter. Robots communicate with each other on a local peer-to-peer
basis and with a server or the cloud via access points, exchanging measurements
and poses to update their belief about the targets and plan future actions. The
server provides a mechanism to collect and synthesize information from all
robots and to share the global, albeit time-delayed, belief state to robots
near access points. We design a decentralized control scheme that exploits this
communication architecture and the PHD representation of the belief state.
Specifically, robots move to maximize mutual information between the target set
and measurements, both self-collected and those available by accessing the
server, balancing local exploration with sharing knowledge across the team.
Furthermore, robots coordinate their actions with other robots exploring the
same local region of the environment.Comment: Extended version of paper accepted to 2013 IEEE International
Conference on Robotics and Automation (ICRA
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