15,338 research outputs found
Drift-Free Indoor Navigation Using Simultaneous Localization and Mapping of the Ambient Heterogeneous Magnetic Field
In the absence of external reference position information (e.g. GNSS) SLAM
has proven to be an effective method for indoor navigation. The positioning
drift can be reduced with regular loop-closures and global relaxation as the
backend, thus achieving a good balance between exploration and exploitation.
Although vision-based systems like laser scanners are typically deployed for
SLAM, these sensors are heavy, energy inefficient, and expensive, making them
unattractive for wearables or smartphone applications. However, the concept of
SLAM can be extended to non-optical systems such as magnetometers. Instead of
matching features such as walls and furniture using some variation of the ICP
algorithm, the local magnetic field can be matched to provide loop-closure and
global trajectory updates in a Gaussian Process (GP) SLAM framework. With a
MEMS-based inertial measurement unit providing a continuous trajectory, and the
matching of locally distinct magnetic field maps, experimental results in this
paper show that a drift-free navigation solution in an indoor environment with
millimetre-level accuracy can be achieved. The GP-SLAM approach presented can
be formulated as a maximum a posteriori estimation problem and it can naturally
perform loop-detection, feature-to-feature distance minimization, global
trajectory optimization, and magnetic field map estimation simultaneously.
Spatially continuous features (i.e. smooth magnetic field signatures) are used
instead of discrete feature correspondences (e.g. point-to-point) as in
conventional vision-based SLAM. These position updates from the ambient
magnetic field also provide enough information for calibrating the
accelerometer and gyroscope bias in-use. The only restriction for this method
is the need for magnetic disturbances (which is typically not an issue
indoors); however, no assumptions are required for the general motion of the
sensor.Comment: ISPRS Workshop Indoor 3D 201
Evolution of isolated turbulent trailing vortices
In this work, the temporal evolution of a low swirl-number turbulent Batchelor vortex is studied using pseudospectral direct numerical simulations. The solution of the governing equations in the vorticity-velocity form allows for accurate application of boundary conditions. The physics of the evolution is investigated with an emphasis on the mechanisms that influence the transport of axial and angular momentum. Excitation of normal mode instabilities gives rise to coherent large scale helical structures inside the vortical core. The radial growth of these helical structures and the action of axial shear and differential rotation results in the creation of a polarized vortex layer. This vortex layer evolves into a series of hairpin-shaped structures that subsequently breakdown into elongated fine scale vortices. Ultimately, the radially outward propagation of these structures results in the relaxation of the flow towards a stable high-swirl configuration. Two conserved quantities, based on the deviation from the laminar solution, are derived and these prove to be useful in characterizing the polarized vortex layer and enhancing the understanding of the transport process. The generation and evolution of the Reynolds stresses is also addressed
A New Era of Legalism for Dispute Settlement Under the WTO
Book review of "Dispute Settlement in the World Trade Organization: Practice and Procedure" by David Palmeter and Petros C. Mavroidis (Boston: Kluwer Law International, 1999).Published in cooperation with the American Bar Association Section of Dispute Resolutio
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