27,077 research outputs found
A Causal And-Or Graph Model for Visibility Fluent Reasoning in Tracking Interacting Objects
Tracking humans that are interacting with the other subjects or environment
remains unsolved in visual tracking, because the visibility of the human of
interests in videos is unknown and might vary over time. In particular, it is
still difficult for state-of-the-art human trackers to recover complete human
trajectories in crowded scenes with frequent human interactions. In this work,
we consider the visibility status of a subject as a fluent variable, whose
change is mostly attributed to the subject's interaction with the surrounding,
e.g., crossing behind another object, entering a building, or getting into a
vehicle, etc. We introduce a Causal And-Or Graph (C-AOG) to represent the
causal-effect relations between an object's visibility fluent and its
activities, and develop a probabilistic graph model to jointly reason the
visibility fluent change (e.g., from visible to invisible) and track humans in
videos. We formulate this joint task as an iterative search of a feasible
causal graph structure that enables fast search algorithm, e.g., dynamic
programming method. We apply the proposed method on challenging video sequences
to evaluate its capabilities of estimating visibility fluent changes of
subjects and tracking subjects of interests over time. Results with comparisons
demonstrate that our method outperforms the alternative trackers and can
recover complete trajectories of humans in complicated scenarios with frequent
human interactions.Comment: accepted by CVPR 201
3D particle tracking velocimetry using dynamic discrete tomography
Particle tracking velocimetry in 3D is becoming an increasingly important
imaging tool in the study of fluid dynamics, combustion as well as plasmas. We
introduce a dynamic discrete tomography algorithm for reconstructing particle
trajectories from projections. The algorithm is efficient for data from two
projection directions and exact in the sense that it finds a solution
consistent with the experimental data. Non-uniqueness of solutions can be
detected and solutions can be tracked individually
AMRA: An Adaptive Mesh Refinement Hydrodynamic Code for Astrophysics
Implementation details and test cases of a newly developed hydrodynamic code,
AMRA, are presented. The numerical scheme exploits the adaptive mesh refinement
technique coupled to modern high-resolution schemes which are suitable for
relativistic and non-relativistic flows. Various physical processes are
incorporated using the operator splitting approach, and include self-gravity,
nuclear burning, physical viscosity, implicit and explicit schemes for
conductive transport, simplified photoionization, and radiative losses from an
optically thin plasma. Several aspects related to the accuracy and stability of
the scheme are discussed in the context of hydrodynamic and astrophysical
flows.Comment: 41 pages, 21 figures (9 low-resolution), LaTeX, requires elsart.cls,
submitted to Comp. Phys. Comm.; additional documentation and high-resolution
figures available from http://www.camk.edu.pl/~tomek/AMRA/index.htm
A Virtual Sky with Extragalactic HI and CO Lines for the SKA and ALMA
We present a sky simulation of the atomic HI emission line and the first ten
CO rotational emission lines of molecular gas in galaxies beyond the Milky Way.
The simulated sky field has a comoving diameter of 500/h Mpc, hence the actual
field-of-view depends on the (user-defined) maximal redshift zmax; e.g. for
zmax=10, the field of view yields ~4x4 sqdeg. For all galaxies, we estimate the
line fluxes, line profiles, and angular sizes of the HI and CO emission lines.
The galaxy sample is complete for galaxies with cold hydrogen masses above 10^8
Msun. This sky simulation builds on a semi-analytic model of the cosmic
evolution of galaxies in a Lambda-cold dark matter (LCDM) cosmology. The
evolving CDM-distribution was adopted from the Millennium Simulation, an N-body
CDM-simulation in a cubic box with a side length of 500/h Mpc. This side length
limits the coherence scale of our sky simulation: it is long enough to allow
the extraction of the baryon acoustic oscillations (BAOs) in the galaxy power
spectrum, yet the position and amplitude of the first acoustic peak will be
imperfectly defined. This sky simulation is a tangible aid to the design and
operation of future telescopes, such the SKA, the LMT, and ALMA. The results
presented in this paper have been restricted to a graphical representation of
the simulated sky and fundamental dN/dz-analyzes for peak flux density limited
and total flux limited surveys of HI and CO. A key prediction is that HI will
be harder to detect at redshifts z>2 than predicted by a no-evolution model.
The future verification or falsification of this prediction will allow us to
qualify the semi-analytic models.Comment: 16 pages, 9 figures, 1 tabl
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