36,776 research outputs found
Ethnographic Research in the U.S. Intelligence Community: Opportunities and Challenges
This article considers lessons learned from conducting research inside the intelligence community. Drawing on a year of ethnographic field work and interviews at the National Counterterrorism Center, I show that “boundary personnel”- people who navigate between the worlds of academia and national security - provide value added in the form of tacit knowledge that outside researchers would not be able to deliver. At the same time, these people face delays, challenges to freedom of information, and ethical considerations that are unique to their positions. Despite setbacks, social scientists must continue their engagement with national security organizations to further our understanding of how these powerful institutions operate
An experimental study of interceptors for drag reduction on high-performance sailing yachts
Interceptors have been widely used in recent years in fast ferries and small high-speed leisure and commercial craft for ride and trim control, and steering. In the context of high-performance sailing yachts, they first appeared in 2008 on the yacht Ecover 3 which was dismasted while leading the Vendee Globe Challenge race. However, in spite of their popularity in power craft, few studies have been published investigating the impact of interceptors on vessel performance, and apparently none in the case of sailing yachts. In the current study, interceptors are compared with an aerodynamic device known as a Gurney flap. It is shown that interceptors are generally substantially smaller than Gurney flaps. A comprehensive experiment programme is presented exploring the impact of interceptors on the performance of an Open 60 yacht hull. Results show a marked reduction in calm-water resistance over a wide speed range, with benefits of 10–18% in the speed range between 8 and 20 knots, accompanied by reduced sinkage and trim. The gains observed are much larger than those observed in powercraft, and also substantially greater than those achievable through trim changes by moving ballast longitudinally. The benefits appear to be largely sustained in small waves
Effects of commercial fishing on local abundance of Pacific cod (Gadus macrocephalus) in the Bering Sea
Groundfish fisheries in the southeast Bering Sea in Alaska
have been constrained in recent years by management measures to protect the endangered Steller sea lion (Eumetopias jubatus). There is concern that the present commercial harvest may produce a localized depletion
of groundfish that would affect the foraging success of Steller sea lions or other predators. A three-year field experiment was conducted to determine whether an intensive
trawl fishery in the southeast Bering Sea created a localized depletion in the abundance of Pacific cod (Gadus
macrocephalus). This experiment produced strongly negative results; no difference was found in the rate of seasonal change in Pacific cod abundance between stations within a
regulatory no-trawl zone and stations in an immediately adjacent trawled area. Corollary studies showed that
Pacific cod in the study area were highly mobile and indicated that the geographic scale of Pacific cod movement
was larger than the spatial scale used as the basis for current no-trawl zones. The idea of localized depletion
is strongly dependent on assumed spatial and temporal scales and contains an implicit assumption that there is
a closed local population. The scale of movement of target organisms is critical in determining regional effects of
fishery removals
ICGC-2004 Conference Overview
This is a written, expanded version of the summary talk given at the
conclusion of the ICGC-2004 held at Cochin. Brief introductory remarks are
included to provide a slightly wider context to the theme talks.Comment: 14 pages, revtex4, no figure
Compliant morphing structures from twisted bulk metallic glass ribbons
In this work, we investigate the use of pre-twisted metallic ribbons as
building blocks for shape-changing structures. We manufacture these elements by
twisting initially flat ribbons about their (lengthwise) centroidal axis into a
helicoidal geometry, then thermoforming them to make this configuration a
stress-free reference state. The helicoidal shape allows the ribbon to have
preferred bending directions that vary throughout its length. These bending
directions serve as compliant joints and enable several deployed and stowed
configurations that are unachievable without pre-twist, provided that
compaction does not induce material failure. We fabricate these ribbons using a
bulk metallic glass (BMG), for its exceptional elasticity and thermoforming
attributes. Combining numerical simulations, an analytical model based on shell
theory and torsional experiments, we analyze the finite-twisting mechanics of
various ribbon geometries. We find that, in ribbons with undulated edges, the
twisting deformations can be better localized onto desired regions prior to
thermoforming. Finally, we join together multiple ribbons to create deployable
systems. Our work proposes a framework for creating fully metallic, yet
compliant structures that may find application as elements for space structures
and compliant robots
Recommended from our members
Evaluating the resilience and security of boundaryless, evolving socio-technical Systems of Systems
- …