1,208 research outputs found
An instrumented tracer for Lagrangian measurements in Rayleigh-B\'enard convection
We have developed novel instrumentation for making Lagrangian measurements of
temperature in diverse fluid flows. A small neutrally buoyant capsule is
equipped with on-board electronics which measure temperature and transmit the
data via a wireless radio frequency link to a desktop computer. The device has
80 dB dynamic range, resolving milli-Kelvin changes in temperature with up to
100 ms sampling time. The capabilities of these "smart particles" are
demonstrated in turbulent thermal convection in water. We measure temperature
variations as the particle is advected by the convective motion, and analyse
its statistics. Additional use of cameras allow us to track the particle
position and to report here the first direct measurement of Lagrangian heat
flux transfer in Rayleigh-B{\'e}nard convection. The device shows promise for
opening new research in a broad variety of fluid systems.Comment: 14 page
Inhibition causes ceaseless dynamics in networks of excitable nodes
The collective dynamics of a network of excitable nodes changes dramatically
when inhibitory nodes are introduced. We consider inhibitory nodes which may be
activated just like excitatory nodes but, upon activating, decrease the
probability of activation of network neighbors. We show that, although the
direct effect of inhibitory nodes is to decrease activity, the collective
dynamics becomes self-sustaining. We explain this counterintuitive result by
defining and analyzing a "branching function" which may be thought of as an
activity-dependent branching ratio. The shape of the branching function implies
that for a range of global coupling parameters dynamics are self-sustaining.
Within the self-sustaining region of parameter space lies a critical line along
which dynamics take the form of avalanches with universal scaling of size and
duration, embedded in ceaseless timeseries of activity. Our analyses, confirmed
by numerical simulation, suggest that inhibition may play a counterintuitive
role in excitable networks.Comment: 11 pages, 6 figure
Summary of Lift and Lift/Cruise Fan Powered Lift Concept Technology
A summary is presented of some of the lift and lift/cruise fan technology including fan performance, fan stall, ground effects, ingestion and thrust loss, design tradeoffs and integration, control effectiveness and several other areas related to vertical short takeoff and landing (V/STOL) aircraft conceptual design. The various subjects addressed, while not necessarily pertinent to specific short takeoff/vertical landing (STOVL) supersonic designs being considered, are of interest to the general field of lift and lift/cruise fan aircraft designs and may be of importance in the future. The various wind tunnel and static tests reviewed are: (1) the Doak VZ-4 ducted fan, (2) the 0.57 scale model of the Bell X-22 ducted fan aircraft, (3) the Avrocar, (4) the General Electric lift/cruise fan, (5) the vertical short takeoff and landing (V/STOL) lift engine configurations related to ingestion and consequent thrust loss, (6) the XV-5 and other fan-in-wing stall consideration, (7) hybrid configurations such as lift fan and lift/cruise fan or engines, and (8) the various conceptual design studies by air-frame contractors. Other design integration problems related to small and large V/STOL transport aircraft are summarized including lessons learned during more recent conceptual design studies related to a small executive V/STOL transport aircraft
Development of a process for continuous dyeing of pet carpet and machnozzle pre-steaming in nylon carpet finishing
Issued as final reportSouthern Company Service
The Effects of Tropical Storm Agnes on Fishes in the James, York, and Rappahannock Rivers of Virginia
Intensive trawl surveys during and after Tropical Storm Agnes were mounted on the James, York, and Rappahannock Rivers to measure the effects of the floodwaters on the distribution and abundance of fish. The direct effect of Agnes on the fish populations was minor and temporary. The normal zone was extended downriver. A substantial portion of the lower-river (marine) species was also displaced downstream and into Chesapeake Bay, but had returned by the follow-up surveys. No adult mortalities due to Agnes were detected. Although we know vast quantities of fish larvae and other plankton were swept into Chesapeake Bay, the overall impact on all fish appears to have been slight.https://scholarworks.wm.edu/vimsbooks/1073/thumbnail.jp
The active pound net fishery in Virginia 1959-1972
An aerial survey of pound nets was conducted in the lower Chesapeake Bay and Virginia rivers from 1959 through 1972. The Potomac River was included from 1965 through 1972. Surveys were conducted monthly, excluding January, during this period.
The pound net is one of the most important fishing gears operated in Virginia waters. A brief description of the net is given. The number of pound nets in the fishery fluctuated from 1959 to 1966, but has been steadily declining since 1966. The term active pound net refers to a stand that has net hanging, and actively fishing at the time of count. Active pound nets are most abundant during spring
Predicting criticality and dynamic range in complex networks: effects of topology
The collective dynamics of a network of coupled excitable systems in response
to an external stimulus depends on the topology of the connections in the
network. Here we develop a general theoretical approach to study the effects of
network topology on dynamic range, which quantifies the range of stimulus
intensities resulting in distinguishable network responses. We find that the
largest eigenvalue of the weighted network adjacency matrix governs the network
dynamic range. Specifically, a largest eigenvalue equal to one corresponds to a
critical regime with maximum dynamic range. We gain deeper insight on the
effects of network topology using a nonlinear analysis in terms of additional
spectral properties of the adjacency matrix. We find that homogeneous networks
can reach a higher dynamic range than those with heterogeneous topology. Our
analysis, confirmed by numerical simulations, generalizes previous studies in
terms of the largest eigenvalue of the adjacency matrix.Comment: 4 pages, 3 figure
Effects of network topology, transmission delays, and refractoriness on the response of coupled excitable systems to a stochastic stimulus
We study the effects of network topology on the response of networks of
coupled discrete excitable systems to an external stochastic stimulus. We
extend recent results that characterize the response in terms of spectral
properties of the adjacency matrix by allowing distributions in the
transmission delays and in the number of refractory states, and by developing a
nonperturbative approximation to the steady state network response. We confirm
our theoretical results with numerical simulations. We find that the steady
state response amplitude is inversely proportional to the duration of
refractoriness, which reduces the maximum attainable dynamic range. We also
find that transmission delays alter the time required to reach steady state.
Importantly, neither delays nor refractoriness impact the general prediction
that criticality and maximum dynamic range occur when the largest eigenvalue of
the adjacency matrix is unity
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