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Cambridge, MA, United States

Dunham E.M.,Stanford University | Belanger D.,BBN Technologies | Kozdon J.E.,Stanford University
Bulletin of the Seismological Society of America | Year: 2011

We study dynamic rupture propagation on flat faults using 2D plane strain models featuring strongly rate-weakening fault friction (in a rate-and-state framework) and off-fault Drucker-Prager viscoplasticity. Plastic deformation bounds stresses near the rupture front and limits slip velocities to ~10 m=s, a bound expected to be independent of earthquake magnitude. As originally shown for ruptures in an elastic medium (Zheng and Rice, 1998), a consequence of strongly rate-weakening friction is the existence of a critical background stress level at which self-sustaining rupture propagation, in the form of self-healing slip pulses, is just barely possible. At higher background stress levels, ruptures are cracklike. This phenomenology remains unchanged when allowing for off-fault plasticity, but the critical stress level is increased. The increase depends on the extent and magnitude of plastic deformation, which is influenced by the orientation of the initial stress field and the proximity of the initial stress state to the yield surface. Source


Pianini D.,University of Bologna | Viroli M.,University of Bologna | Beal J.,BBN Technologies
Proceedings of the ACM Symposium on Applied Computing | Year: 2015

The notion of a computational field has been proposed as a unifying abstraction for developing distributed systems, focusing on the computations and coordination of aggregates of devices instead of individual behavior. Prior field-based languages, however, have suffered from a number of practical limitations that have posed barriers to adoption and use. We address these limitations by introduction of Protelis, a functional language based on computational fields and embedded in Java, thereby enabling the construction of widely reusable components of aggregate systems. We demonstrate the simplicity of Protelis integration and programming through two examples: simulation of a pervasive computing scenario in the Alchemist simulator [24], and coordinated management of a network of services. Copyright 2015 ACM. Source


Beal J.,BBN Technologies
Swarm Intelligence | Year: 2011

The engineering of grown systems poses fundamentally different system integration challenges than ordinary engineering of static designs. On the one hand, a grown system must be capable of surviving not only in its final form, but at every intermediate stage, despite the fact that its subsystems may grow unevenly or be subject to different scaling laws. On the other hand, the ability to grow offers much greater potential for adaptation, either to changes in the environment or to internal stresses developed as the system grows. I observe that the ability of subsystems to tolerate stress can be used to transform incremental adaptation into the dynamic discovery of viable growth trajectories for the system as a whole. Using this observation, I propose an engineering approach based on functional blueprints, under which a system is specified in terms of desired performance and means of incrementally correcting deficiencies. I explore how manifold geometric programming can support such an approach by simplifying the construction of distortion-tolerant programs, then demonstrate the functional blueprints approach by applying it to integrate simplified models of tissue growth and vascularization, and further show how the composed system may itself be modulated for use as a component in a more complex design. © 2011 Springer Science + Business Media, LLC. Source


Barnes R.,BBN Technologies
IEEE Communications Magazine | Year: 2011

As the edge of the Internet becomes increasingly mobile, location-based Internet applications have taken on a much more prominent role. At the same time, though, the underlying geolocation systems that support these applications were designed with specific circumstances in mind, rather than being general to the whole Internet. The IETF GEOPRIV architecture provides a unified geolocation system for the Internet, allowing applications to benefit from current geolocation design patterns as well as some new security and privacy features. © 2006 IEEE. Source


Feurzeig W.,BBN Technologies
International Journal of Computers for Mathematical Learning | Year: 2010

This paper describes the creation and early uses of Logo. It includes a brief summary of more recent work on Logo-derived languages and learning applications. It closes with a lament on the unrealized potential of student programming languages as empowering tools for knowledge construction and learning. © 2010 Springer Science+Business Media B.V. Source

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