7,251 research outputs found
Lattices of hydrodynamically interacting flapping swimmers
Fish schools and bird flocks exhibit complex collective dynamics whose
self-organization principles are largely unknown. The influence of
hydrodynamics on such collectives has been relatively unexplored theoretically,
in part due to the difficulty in modeling the temporally long-lived
hydrodynamic interactions between many dynamic bodies. We address this through
a novel discrete-time dynamical system (iterated map) that describes the
hydrodynamic interactions between flapping swimmers arranged in one- and
two-dimensional lattice formations. Our 1D results exhibit good agreement with
previously published experimental data, in particular predicting the
bistability of schooling states and new instabilities that can be probed in
experimental settings. For 2D lattices, we determine the formations for which
swimmers optimally benefit from hydrodynamic interactions. We thus obtain the
following hierarchy: while a side-by-side single-row "phalanx" formation offers
a small improvement over a solitary swimmer, 1D in-line and 2D rectangular
lattice formations exhibit substantial improvements, with the 2D diamond
lattice offering the largest hydrodynamic benefit. Generally, our
self-consistent modeling framework may be broadly applicable to active systems
in which the collective dynamics is primarily driven by a fluid-mediated
memory
Ready or Not? Protecting the Public's Health in the Age of Bioterrorism, 2004
Examines ten key indicators to evaluate state preparedness to respond to bioterrorist attacks and other public health emergencies. Evaluates the federal government's role and performance, and offers recommendations for improving readiness
A Review and Research Suggestions for Empirical Approaches to Evaluating Reinforcing Effects of Peer Attention vs. Teacher Attention in the General Education Classroom
Behavior management in the general education classroom can be difficult at times for educators. Attention is one reinforcer of children\u27s behavior in the classroom and the child\u27s behavior may be maintained by teacher attention or peer attention. If attentions is implemented appropriately, peer or teacher attention may prove to be an effective reinforcer in maintaining appropriate behaviors in the classroom. Teacher attention is commonly used to maintain student performance (Broussard & Northup, 1997). Educators may not know which is more reinforcing to the typical student in the general education classroom - teacher attention or peer attention. However, evaluating the effectiveness of such a reinforcer involves evaluating the preference for an intervention, rather than a specific stimulus that can be arranged in a traditional stimulus preference assessment (Hagopian, Long, &Rush, 2004; Hanley, Iwata, & Lindberg, 1999). A modified concurrent-chains assessment can be used to determine the reinforcer preference of individuals (Hanley, 2010). This paper will summarize the use of a modified concurrent-chains assessment on typical students in the general education classroom in order to determine students\u27 preference of peer attention vs. teacher attention
Instructional Leadership, Teaching Quality, and Student Achievement: Suggestive Evidence from Three Urban School Districts
Does providing instruction-related professional development to school principals set in motion a chain of events that can improve teaching and learning in their schools? This report examines professional development efforts by the University of Pittsburgh's Institute for Learning in elementary schools in Austin, St. Paul, and New York City
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