141,286 research outputs found
Exploiting short-term memory in soft body dynamics as a computational resource
Soft materials are not only highly deformable but they also possess rich and
diverse body dynamics. Soft body dynamics exhibit a variety of properties,
including nonlinearity, elasticity, and potentially infinitely many degrees of
freedom. Here we demonstrate that such soft body dynamics can be employed to
conduct certain types of computation. Using body dynamics generated from a soft
silicone arm, we show that they can be exploited to emulate functions that
require memory and to embed robust closed-loop control into the arm. Our
results suggest that soft body dynamics have a short-term memory and can serve
as a computational resource. This finding paves the way toward exploiting
passive body dynamics for control of a large class of underactuated systems.Comment: 22 pages, 11 figures; email address correcte
Learning Particle Dynamics for Manipulating Rigid Bodies, Deformable Objects, and Fluids
Real-life control tasks involve matters of various substances---rigid or soft
bodies, liquid, gas---each with distinct physical behaviors. This poses
challenges to traditional rigid-body physics engines. Particle-based simulators
have been developed to model the dynamics of these complex scenes; however,
relying on approximation techniques, their simulation often deviates from
real-world physics, especially in the long term. In this paper, we propose to
learn a particle-based simulator for complex control tasks. Combining learning
with particle-based systems brings in two major benefits: first, the learned
simulator, just like other particle-based systems, acts widely on objects of
different materials; second, the particle-based representation poses strong
inductive bias for learning: particles of the same type have the same dynamics
within. This enables the model to quickly adapt to new environments of unknown
dynamics within a few observations. We demonstrate robots achieving complex
manipulation tasks using the learned simulator, such as manipulating fluids and
deformable foam, with experiments both in simulation and in the real world. Our
study helps lay the foundation for robot learning of dynamic scenes with
particle-based representations.Comment: Accepted to ICLR 2019. Project Page: http://dpi.csail.mit.edu Video:
https://www.youtube.com/watch?v=FrPpP7aW3L
Statics and Dynamics of Strongly Charged Soft Matter
Soft matter materials, such as polymers, membranes, proteins, are often
electrically charged. This makes them water soluble, which is of great
importance in technological application and a prerequisite for biological
function. We discuss a few static and dynamic systems that are dominated by
charge effects. One class comprises complexation between oppositely charged
objects, for example the adsorption of charged ions or charged polymers (such
as DNA) on oppositely charged substrates of different geometry. The second
class comprises effective interactions between similarly charged objects. Here
the main theme is to understand the experimental finding that similarly and
highly charged bodies attract each other in the presence of multi-valent
counterions. This is demonstrated using field-theoretic arguments as well as
Monte-Carlo simulations for the case of two homogeneously charged bodies.
Realistic surfaces, on the other hand, are corrugated and also exhibit
modulated charge distributions, which is important for static properties such
as the counterion-density distribution, but has even more pronounced
consequences for dynamic properties such as the counterion mobility. More
pronounced dynamic effects are obtained with highly condensed charged systems
in strong electric fields. Likewise, an electrostatically collapsed highly
charged polymer is unfolded and oriented in strong electric fields. At the end
of this review, we give a very brief account of the behavior of water at planar
surfaces and demonstrate using ab-initio methods that specific interactions
between oppositely charged groups cause ion-specific effects that have recently
moved into the focus of interest.Comment: 61 pages, 31 figures, Physics Reports (2005)-in press (high quality
figures available from authors
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The telematic dress: Evolving garments and distributed proprioception in streaming media and fashion performance
Centered around several short films from streaming performances created in 2005, this paper
explores new ideas for movement technologies and garment design in an arts and digital research
context. The "telematic dress" project, developed at the DAP Lab in Nottingham, involves
transdisciplinary intersections between fashion and live performance, interactive system architecture,
electronic textiles, wearable technologies, choreography, and anthropology.
The concept on an evolving garment design that is materialized (moved) in live performance
originates from DAP Lab's experimentation with telematics and distributed media (http://art.ntu.ac.
uk/performance_research/birringer/dap.htm] addressing "connective tissues" through a study of
perception/proprioception in the wearer (tactile sensory processing) and the dancer/designer/viewer
relationship. This study is conducted as cross-cultural communication with online performance
partners in Europe, the US, Brazil and Japan. The inter-active space is predicated on transcultural
questions: how does the movement with an evolving design and wearable interactive sensors travel,
how does movement - and capturing of movement - allow the design to emerge toward a garment
statement, and how are bodies-in-relation-to sensory fabrics affected by the multidimensional
kinesthetics of a media-rich, responsive environment
Optimal control of the heave motion of marine cable subsea-unit systems
One of the key problems associated with subsea operations involving tethered subsea units is the motions of support vessels on the ocean surface which can be transmitted to the subsea unit through the cable and increase the tension. In this paper, a theoretical approach for heave compensation is developed. After proper modelling of each element of the system, which includes the cable/subsea-unit, the onboard winch, control theory is applied to design an optimal control law. Numerical simulations are carried out, and it is found that the proposed active control scheme appears to be a promising solution to the problem of heave compensation
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Fatty acid bioaccessibility and structural breakdown from in vitro digestion of almond particles.
Previous studies have shown that the size of almond particles influences lipid bioaccessibility during digestion. However, the extent of structural breakdown of almond particles during gastric digestion and its impact on lipid bioaccessibility is unclear. In this study, in vitro digestion of almond particles was conducted using a dynamic model (Human Gastric Simulator) and a static model (shaking water bath). Structural breakdown of particles during the gastric phase occurred only in the Human Gastric Simulator, as evidenced by a reduction in particle size (15.89 ± 0.68 mm2 to 12.19 ± 1.29 mm2, p < 0.05). Fatty acid bioaccessibility at the end of the gastric phase was greater in the Human Gastric Simulator than in the shaking water bath (6.55 ± 0.85% vs. 4.54 ± 0.36%, p < 0.01). Results showed that the in vitro model of digestion which included peristaltic contractions (Human Gastric Simulator) led to breakdown of almond particles during gastric digestion which increased fatty acid bioaccessibility
Evaluating affordances of streams and rivers pertaining to children functioning in natural environment
This study evaluates the affordances of natural water bodies pertaining to functioning of children. Ten children, aged 4-12, were observed experiencing three streams and two rivers in tropical environment. A phenomenological approach yielded a dataset of the children’s behavioral responses derived from a behavioral mapping and an open-ended interview. The responses are physical movement and words and phrases of the children suggesting their preferences or dislikes toward the water settings. The data was analyzed in three stages, firstly, positive or negative affordances, secondly, a taxonomy affordance of children’s outdoor environment, and thirdly, level of affordances. The children experienced 78 positive affordances and only five negative ones. From the taxonomy, the water afforded 11 categories of environmental qualities in which the categories graspable/detached objects and water offered the most number of affordances, 16 and 15, respectively. Most of the children’s activities were performatory and exploratory types. The results suggest that children perceived the affordances of streams and rivers through physical, cognitive and social interactions. The children, therefore, perceived the water bodies as playscapes affording varieties of functional meanings
Analysis of piezocone penetration under different drainage conditions with the two-phase Material Point Method
The piezocone penetration test (CPTU) is commonly used to identify the soil profile and to estimate material properties. Depending on the soil type, ranging from clay to sand, undrained, partially drained or drained conditions may occur during cone penetration. In silt and sand-clay mixtures the CPTU penetration is characterized by partially drained conditions, which are often neglected in data interpretation. The effect of drainage on CPTU measurements has been mainly studied experimentally. Numerical analyses are rare because taking into account large soil deformations, soil-water and soil-structure interactions, as well as non-linear soil behaviour is still a challenging task. This paper presents and discusses numerical simulations of CPTU in saturated soils with the two-phase Material Point Method. Soil behaviour is described with the Modified Cam Clay model. This study investigates the effects of pore pressure dissipation during penetration, cone roughness and horizontal stress state, comparing the results with experimental data. The paper discusses the effect of neglecting partial drainage in deriving the shear strength parameters for silty soils and suggests a procedure to estimate the consolidation coefficient performing CPTU at different penetration rates
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