94,919 research outputs found
Sensory Motor Remapping of Space in Human-Machine Interfaces
Studies of adaptation to patterns of deterministic forces have revealed the ability of the motor control system to form and use predictive representations of the environment. These studies have also pointed out that adaptation to novel dynamics is aimed at preserving the trajectories of a controlled endpoint, either the hand of a subject or a transported object. We review some of these experiments and present more recent studies aimed at understanding how the motor system forms representations of the physical space in which actions take place. An extensive line of investigations in visual information processing has dealt with the issue of how the Euclidean properties of space are recovered from visual signals that do not appear to possess these properties. The same question is addressed here in the context of motor behavior and motor learning by observing how people remap hand gestures and body motions that control the state of an external device. We present some theoretical considerations and experimental evidence about the ability of the nervous system to create novel patterns of coordination that are consistent with the representation of extrapersonal space. We also discuss the perspective of endowing human–machine interfaces with learning algorithms that, combined with human learning, may facilitate the control of powered wheelchairs and other assistive devices
Cell reorientation under cyclic stretching
Mechanical cues from the extracellular microenvironment play a central role
in regulating the structure, function and fate of living cells. Nevertheless,
the precise nature of the mechanisms and processes underlying this crucial
cellular mechanosensitivity remains a fundamental open problem. Here we provide
a novel framework for addressing cellular sensitivity and response to external
forces by experimentally and theoretically studying one of its most striking
manifestations -- cell reorientation to a uniform angle in response to cyclic
stretching of the underlying substrate. We first show that existing approaches
are incompatible with our extensive measurements of cell reorientation. We then
propose a fundamentally new theory that shows that dissipative relaxation of
the cell's passively-stored, two-dimensional, elastic energy to its minimum
actively drives the reorientation process. Our theory is in excellent
quantitative agreement with the complete temporal reorientation dynamics of
individual cells, measured over a wide range of experimental conditions, thus
elucidating a basic aspect of mechanosensitivity.Comment: For supplementary materials, see
http://www.nature.com/ncomms/2014/140530/ncomms4938/extref/ncomms4938-s1.pd
Virtual Testing of Experimental Continuation
We present a critical advance in experimental testing of nonlinear
structures. Traditional quasi-static experimental methods control the
displacement or force at one or more load-introduction points on a structure.
This approach is unable to traverse limit points in the control parameter, as
the immediate equilibrium beyond these points is statically unstable, causing
the structure to snap to another equilibrium. As a result, unstable
equilibria---observed numerically---are yet to be verified experimentally.
Based on previous experimental work, and a virtual testing environment
developed herein, we propose a new experimental continuation method that can
path-follow along unstable equilibria and traverse limit points. To support
these developments, we provide insightful analogies between a fundamental
building block of our technique---shape control---and analysis concepts such as
the principle of virtual work and Galerkin's method. The proposed testing
method will enable the validation of an emerging class of nonlinear structures
that exploit instabilities for novel functionality
Calipso: Physics-based Image and Video Editing through CAD Model Proxies
We present Calipso, an interactive method for editing images and videos in a
physically-coherent manner. Our main idea is to realize physics-based
manipulations by running a full physics simulation on proxy geometries given by
non-rigidly aligned CAD models. Running these simulations allows us to apply
new, unseen forces to move or deform selected objects, change physical
parameters such as mass or elasticity, or even add entire new objects that
interact with the rest of the underlying scene. In Calipso, the user makes
edits directly in 3D; these edits are processed by the simulation and then
transfered to the target 2D content using shape-to-image correspondences in a
photo-realistic rendering process. To align the CAD models, we introduce an
efficient CAD-to-image alignment procedure that jointly minimizes for rigid and
non-rigid alignment while preserving the high-level structure of the input
shape. Moreover, the user can choose to exploit image flow to estimate scene
motion, producing coherent physical behavior with ambient dynamics. We
demonstrate Calipso's physics-based editing on a wide range of examples
producing myriad physical behavior while preserving geometric and visual
consistency.Comment: 11 page
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