Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct multi-scale reconstruction of velocity fields from measurements
  of particle tracks   We present a method for reconstructing two-dimensional velocity fields at
specified length scales using observational data from tracer particles in a
flow, without the need for interpolation or smoothing. The algorithm, adapted
from techniques proposed for oceanography, involves a least-squares projection
of the measurements onto a set of two-dimensional, incompressible basis modes
with known length scales. Those modes are constructed from components of the
velocity potential function, which accounts for inflow and outflow at the open
boundaries of the measurement region; and components of the streamfunction,
which accounts for the remainder of the flow. All calculations are evaluated at
particle locations, without interpolation onto an arbitrary grid. Since the
modes have a well-defined length scales, scale-local flow properties are
available directly. The technique eliminates outlier particles automatically
and reduces the apparent compressibility of the data. Moreover the technique
can be used to produce spatial power spectra and to evaluate the spatial
effects of open boundaries; it also holds promise for direct calculation of
scale-to-scale transfer of enstrophy and energy.

11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin