A Neural Circuit for Coordinating Reaching with Grasping: Autocompensating Variable Initial Apertures, Perturbations to Target Size, and Perturbations to Target Orientation

A neural network model is presented, that extends principles of the VITE (vector integration to end-point) model [1, 2, 3, 4] of primate reaching to the more complex case of reach-grasp coordination. The main new planning problem addressed by the model is how to simulate human data on temporal coordination between reaching and grasping, while at the same time remaining stable and compensating for altered initial apertures and perturbations of object size and object location/ orientation. Simulations of the model replicate key features of four different experimental protocols with a single set of parameters. The proposed circuit computes reaching to grasp trajectories in real-time, by continuously updating vector positioning commands, and with no precomputation of total or component movement times. The model consists of three generator channels: transport, which generates a reaching trajectory; aperture, which controls distance between thumb and index finger; and orientation, which controls hand orientation vis-a-vis target's orientation.CONACYT of Mexico; Defense Advanced Research Projects Agency and Office of Naval Research (N00014-95-1-0409

A Neural Circuit for Coordinating Reaching with Grasping: Autocompensating Variable Initial Apertures, Perturbations to Target Size, and Perturbations to Target Orientation

A neural network model is presented, that extends principles of the VITE (vector integration to end-point) model [1, 2, 3, 4] of primate reaching to the more complex case of reach-grasp coordination. The main new planning problem addressed by the model is how to simulate human data on temporal coordination between reaching and grasping, while at the same time remaining stable and compensating for altered initial apertures and perturbations of object size and object location/ orientation. Simulations of the model replicate key features of four different experimental protocols with a single set of parameters. The proposed circuit computes reaching to grasp trajectories in real-time, by continuously updating vector positioning commands, and with no precomputation of total or component movement times. The model consists of three generator channels: transport, which generates a reaching trajectory; aperture, which controls distance between thumb and index finger; and orientation, which controls hand orientation vis-a-vis target's orientation.CONACYT of Mexico; Defense Advanced Research Projects Agency and Office of Naval Research (N00014-95-1-0409

Inhomogeneities and caustics in the sedimentation of noninertial particles in incompressible flows

In an incompressible flow, fluid density remains invariant along fluid element trajectories. This implies that the spatial distribution of non-interacting noninertial particles in such flows cannot develop density inhomogeneities beyond those that are already introduced in the initial condition. However, in certain practical situations, density is measured or accumulated on (hyper-) surfaces of dimensionality lower than the full dimensionality of the flow in which the particles move. An example is the observation of particle distributions sedimented on the floor of the ocean. In such cases, even if the initial distribution of noninertial particles is uniform within a finite support in an incompressible flow, advection in the flow will give rise to inhomogeneities in the observed density. In this paper we analytically derive, in the framework of an initially homogeneous particle sheet sedimenting towards a bottom surface, the relationship between the geometry of the flow and the emerging distribution. From a physical point of view, we identify the two processes that generate inhomogeneities to be the stretching within the sheet, and the projection of the deformed sheet onto the target surface. We point out that an extreme form of inhomogeneity, caustics, can develop for sheets. We exemplify our geometrical results with simulations of particle advection in a simple kinematic flow, study the dependence on various parameters involved, and illustrate that the basic mechanisms work similarly if the initial (homogeneous) distribution occupies a more general region of finite extension rather than a sheet.Comment: 56 pages, 17 figure

An Overview of Moving Object Trajectory Compression Algorithms

Compression technology is an efficient way to reserve useful and valuable data as well as remove redundant and inessential data from datasets. With the development of RFID and GPS devices, more and more moving objects can be traced and their trajectories can be recorded. However, the exponential increase in the amount of such trajectory data has caused a series of problems in the storage, processing, and analysis of data. Therefore, moving object trajectory compression undoubtedly becomes one of the hotspots in moving object data mining. To provide an overview, we survey and summarize the development and trend of moving object compression and analyze typical moving object compression algorithms presented in recent years. In this paper, we firstly summarize the strategies and implementation processes of classical moving object compression algorithms. Secondly, the related definitions about moving objects and their trajectories are discussed. Thirdly, the validation criteria are introduced for evaluating the performance and efficiency of compression algorithms. Finally, some application scenarios are also summarized to point out the potential application in the future. It is hoped that this research will serve as the steppingstone for those interested in advancing moving objects mining

Self-assembly of Active Colloidal Molecules with Dynamic Function

Catalytically active colloids maintain non-equilibrium conditions in which they produce and deplete chemicals and hence effectively act as sources and sinks of molecules. While individual colloids that are symmetrically coated do not exhibit any form of dynamical activity, the concentration fields resulting from their chemical activity decay as $1/r$ and produce gradients that attract or repel other colloids depending on their surface chemistry and ambient variables. This results in a non-equilibrium analogue of ionic systems, but with the remarkable novel feature of action-reaction symmetry breaking. We study solutions of such chemically active colloids in dilute conditions when they join up to form molecules via generalized ionic bonds, and discuss how we can achieve structures with time dependent functionality. In particular, we study a molecule that adopts a spontaneous oscillatory pattern of conformations, and another that exhibits a run-and-tumble dynamics similar to bacteria. Our study shows that catalytically active colloids could be used for designing self-assembled structures that posses dynamical functionalities that are determined by their prescribed 3D structures, a strategy that follows the design principle of proteins