This paper addresses the problem of detecting coherent motions in crowd scenes and subsequently constructing semantic regions for activity recognition. We first introduce a coarse-to-fine thermal-diffusionbased approach. It processes input motion fields (e.g., optical flow fields) and produces a coherent motion filed, named as thermal energy field. The thermal energy field is able to capture bo...

The optzcal floul constitutes one of the most widely adopted representatzons to define and characterzze the evolutzon of image features over time. In order to compute the velocity field, it is necessary to define a set of constraints on the temporal change of image features. In this paper we consider the implications in using multiple constraints arising f rom multiple d a t a points. The first...

We analyze vorticity fields obtained from direct numerical simulations (DNS) of statistically stationary two-dimensional turbulence where the forcing is done in wavelet space. We introduce a new eduction method for extracting coherent structures from two-dimensional turbulent flows. Using a nonlinear wavelet technique based on an objective universal threshold we separate the vorticity field int...

The notions of Finite-Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures provide a strong framework for the analysis and visualization of complex technical flows. Their definition is simple and intuitive, and they are built on a deep theoretical foundation. We apply these concepts to enable the analysis of flows in the immediate vicinity of the boundaries of flow-embedded objects ...

This paper presents the application of coherent vortex simulation (CVS) filtering, based on an orthogonal wavelet decomposition of vorticity, to study mixing in 2D homogeneous isotropic turbulent flows. The Eulerian and Lagrangian dynamics of the flow are studied by comparing the evolution of a passive scalar and of particles advected by the coherent and incoherent velocity fields, respectively...

We study coherent structures in solar photospheric flows in a plage in the vicinity of the active region AR 10930 using the horizontal velocity data derived from Hinode/Solar Optical Telescope magnetograms. Eulerian and Lagrangian coherent structures (LCSs) are detected by computing the Q-criterion and the finite-time Lyapunov exponents of the velocity field, respectively. Our analysis indicate...

Locally parallel dense patterns sometimes called texture flows define a perceptually coherent structure which is important to image segmentation, edge classification, shading analysis, and shape interpretation. This paper develops the notion of texture flow from a geometrical point of view to argue that local measurements of such structures must incorporate two curvatures. We show how basic the...

The discrete wavelet transform (DWT) and discrete wavelet packet transform (DWPT) are used to extract and study the dynamics of coherent structures in a turbulent rotating fluid. Three-dimensional turbulence is generated by strong pumping through tubes at the bottom of a rotating tank (48.4 cm high, 39.4 cm diameter). This flow evolves toward two-dimensional (2D) turbulence with increasing heig...

This is an excerpt fromMathematisches Forschungsinstitut Oberwolfach Report 4/2014, doi: 10.4171/OWR/2014/4, which contained extended abstracts from the Workshop on Mixing, Transport and Coherent Structures held at Oberwolfach in January, 2014. This extended abstract takes a broad and critical view on the existing methods on determining flow barriers in unsteady flows, while also calling for ex...

The concept of coherent structure in turbulent flow is a revolutionary idea which is being developed by evolutionary •eans. The aain objective of this review iR to list so•e solid achieve•ent1, showing what can be done by using the concept of coherent structure that cannot be done without it . The nature of structure is described in terns of so•e related concepts , including celerity. topology....