Discovery and recognition of motion primitives in human activities

We present a novel framework for the automatic discovery and recognition of motion primitives in videos of human activities. Given the 3D pose of a human in a video, human motion primitives are discovered by optimizing the `motion flux', a quantity which captures the motion variation of a group of skeletal joints. A normalization of the primitives is proposed in order to make them invariant with respect to a subject anatomical variations and data sampling rate. The discovered primitives are unknown and unlabeled and are unsupervisedly collected into classes via a hierarchical non-parametric Bayes mixture model. Once classes are determined and labeled they are further analyzed for establishing models for recognizing discovered primitives. Each primitive model is defined by a set of learned parameters. Given new video data and given the estimated pose of the subject appearing on the video, the motion is segmented into primitives, which are recognized with a probability given according to the parameters of the learned models. Using our framework we build a publicly available dataset of human motion primitives, using sequences taken from well-known motion capture datasets. We expect that our framework, by providing an objective way for discovering and categorizing human motion, will be a useful tool in numerous research fields including video analysis, human inspired motion generation, learning by demonstration, intuitive human-robot interaction, and human behavior analysis

Hidden Invariants in Rheology: The Persistent Granular Nature of Liquids

This article will use arguments derived from the deformation driven component of mixing, especially important for microfluidics, to show that the standard invariant based approaches to rheology are lacking. It is shown that the deviator, $D_{ij}$, after the process of symmetrization, loses microscopically determined information that distinguish rotation from shear and extension in a unique fashion. We recover this information through an analysis of the discrete processes that must underlie deformation driven mixing in highly correlated fluids. Without this we show there is no hope of ever deriving adequate general material parameters for rheology from microscopic dynamics. There is an unambiguous microscopic notion of the rotation rate for every parcel and we derive a general class of invariant rheological theories from it. We discuss some implications of higher order flows on solutions and suspensions including possibilities for driving and stabilization of nonuniform distributions using hydrodynamic forces alone

Experimental investigation on self-similar heat sinks for liquid cooled electronics

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The high heat transfer coefficients in microchannels are attractive for direct cooling of electronic systems requiring high heat-flux removal. In this work we are presenting the results of a study on self-similar heat sinks for liquid cooled electronics, made from copper, designed for industrial application and for large scale production. The internal structures, where the most part of the active cooling takes place, have been designed in order to achieve high heat transfer coefficients. As it is almost impossible to validate the design and describe the flow characteristics inside the device via analytical solutions, a well known numerical code was employed to have an insight of the thermal-fluid distributions. It is clear from the simulation that even if copper is characterized by a high thermal conductivity, most of the heat is removed in the overflow-structure, on the side of the device adjacent to the source of heat. This paper attempts to critically analyse a comprehensive list of data as well as plots in order to illustrate the significant characteristics of this type of device

c-extremization from toric geometry

We derive a geometric formulation of the 2d central charge $c_r$ from infinite families of 4d $\mathcal{N}=1$ superconformal field theories topologically twisted on constant curvature Riemann surfaces. They correspond to toric quiver gauge theories and are associated to D3 branes probing five dimensional Sasaki-Einstein geometries in the AdS/CFT correspondence. We show that $c_r$ can be expressed in terms of the areas of the toric diagram describing the moduli space of the 4d theory, both for toric geometries with smooth and singular horizons. We also study the relation between a-maximization in 4d and c-extremization in 2d, giving further evidences of the mixing of the baryonic symmetries with the exact R-current in two dimensions.Comment: 39 pages, 21 figures, minor change

Constraining Intra-cluster Gas Models with AMiBA13

Clusters of galaxies have been used extensively to determine cosmological parameters. A major difficulty in making best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement (AMR) cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intra-cluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2-m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal beta models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.Comment: Accepted for publication in The Astrophysical Journal, 12 pages, 9 figure