16,404 research outputs found
Body-rock or lift-off in flow
Conditions are investigated under which a body lying at rest or rocking on a
solid horizontal surface can be removed from the surface by hydrodynamic forces
or instead continues rocking. The investigation is motivated by recent
observations on Martian dust movement as well as other small- and large-scale
applications. The nonlinear theory of fluid-body interaction here has unsteady
motion of an inviscid fluid interacting with a moving thin body. Various shapes
of body are addressed together with a range of initial conditions. The relevant
parameter space is found to be subtle as evolution and shape play substantial
roles coupled with scaled mass and gravity effects. Lift-off of the body from
the surface generally cannot occur without fluid flow but it can occur either
immediately or within a finite time once the fluid flow starts up: parameters
for this are found and comparisons are made with Martian observations.Comment: 28 pages, 9 figure
Explanation and Cognition
These essays draw on work in the history and philosophy of science, the philosophy of mind and language, the development of concepts in children, conceptual.
ARTMAP-DS: Pattern Discrimination by Discounting Similarities
ARTMAP-DS extends fuzzy ARTMAP to discriminate between similar inputs by discounting similarities. When two or more candidate category representations are activated by a given input, features that the candidate representations have in common are ignored prior to determining the winning category. Simulations illustrate the network's ability to recognize similar inputs, such as STAR and START, in a noisy environment.National Science Foundation (IRI-94-01659); Office of Naval Research (N00014-95-1-0409, N00014-95-1-0657
Explaining Explanation
It is not a particularly hard thing to want or seek explanations. In fact, explanations seem to be a large and natural part of our cognitive lives. Children ask why and how questions very early in development and seem genuinely to want some sort of answer, despite our often being poorly equipped to provide them at the appropriate level of sophistication and detail. We seek and receive explanations in every sphere of our adult lives, whether it be to understand why a friendship has foundered, why a car will not start, or why ice expands when it freezes. Moreover, correctly or incorrectly, most of the time we think we know when we have or have not received a good explanation. There is a sense both that a given, successful explanation satisfies a cognitive need, and that a questionable or dubious explanation does not. There are also compelling intuitions about what make good explanations in terms of their form, that is, a sense of
when they are structured correctly
Vortex motion phase separator for zero gravity liquid transfer
A vortex motion phase separator is disclosed for transferring a liquid in a zero gravity environment while at the same time separating the liquid from vapors found within either the sender or the receiving tanks. The separator comprises a rigid sender tank having a circular cross-section and rigid receiver tank having a circular cross-section. A plurality of ducts connects the sender tank and the receiver tank. Disposed within the ducts connecting the receiver tank and the sender tank is a pump and a plurality of valves. The pump is powered by an electric motor and is adapted to draw either the liquid or a mixture of the liquid and the vapor from the sender tank. Initially, the mixture drawn from the sender tank is directed through a portion of the ductwork and back into the sender tank at a tangent to the inside surface of the sender tank, thereby creating a swirling vortex of the mixture within the sender tank. As the pumping action increases, the speed of the swirling action within the sender tank increases creating an increase in the centrifugal force operating on the mixture. The effect of the centrifugal force is to cause the heavier liquid to migrate to the inside surface of the sender tank and to separate from the vapor. When this separation reaches a predetermined degree, control means is activated to direct the liquid conveyed by the pump directly into the receiver tank. At the same time, the vapor within the receiver tank is directed from the receiver tank back into the sender tank. This flow continues until substantially all of the liquid is transferred from the sender tank to the receiver tank
Segmentation ART: A Neural Network for Word Recognition from Continuous Speech
The Segmentation ATIT (Adaptive Resonance Theory) network for word recognition from a continuous speech stream is introduced. An input sequeuce represents phonemes detected at a preproccesing stage. Segmentation ATIT is trained rapidly, and uses a fast-learning fuzzy ART modules, top-down expectation, and a spatial representation of temporal order. The network performs on-line identification of word boundaries, correcting an initial hypothesis if subsequent phonemes are incompatible with a previous partition. Simulations show that the system's segmentation perfonnance is comparable to that of TRACE, and the ability to segment a number of difficult phrases is also demonstrated.National Science Foundation (NSF-IRI-94-01659); Office of Naval Research (N00014-95-1-0409, N00014-95-1-0G57
Biology, Injury, and Control of the European Needle-bending Midge (Diptera: Cecidomyiidae) on Scotch Pine in Michigan
Contarinia baeri is univoltine in Michigan. Adults emerge in spring, and females deposit eggs in small clusters in the sheaths of new-growth pine needles. Larvae hatch shortly thereafter and there are three larval instars. Larval feeding causes the needles to at first droop, discolor, and eventually drop, reducing the quality of Christmas trees and occasionally killing shoots. Larvae overwinter on the ground in cocoons, and pupate in spring. Adults were suppressed (\u3e 75% control) with formulations of Pydrin® (fenvalerate) and Tempo® (cyfluthrin) applied within a week after adult emergence
A general model of the public goods dilemma
An individually costly act that benefits all group members is a public good.
Natural selection favors individual contribution to public goods only when some
benefit to the individual offsets the cost of contribution. Problems of sex
ratio, parasite virulence, microbial metabolism, punishment of noncooperators,
and nearly all aspects of sociality have been analyzed as public goods shaped
by kin and group selection. Here, I develop two general aspects of the public
goods problem that have received relatively little attention. First, variation
in individual resources favors selfish individuals to vary their allocation to
public goods. Those individuals better endowed contribute their excess
resources to public benefit, whereas those individuals with fewer resources
contribute less to the public good. Thus, purely selfish behavior causes
individuals to stratify into upper classes that contribute greatly to public
benefit and social cohesion and to lower classes that contribute little to the
public good. Second, if group success absolutely requires production of the
public good, then the pressure favoring production is relatively high. By
contrast, if group success depends weakly on the public good, then the pressure
favoring production is relatively weak. Stated in this way, it is obvious that
the role of baseline success is important. However, discussions of public goods
problems sometimes fail to emphasize this point sufficiently. The models here
suggest simple tests for the roles of resource variation and baseline success.
Given the widespread importance of public goods, better models and tests would
greatly deepen our understanding of many processes in biology and sociality
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