16,950 research outputs found
Biological Assessments of Six Selected Fishes, Amphibians, and Mussels in Illinois
ID: 8758; issued November 1, 1996INHS Technical Report prepared for Illinois Department of Natural Resources, Division of
Natural Heritag
Ultracold neutral plasma expansion in two dimensions
We extend an isothermal thermal model of ultracold neutral plasma expansion
to systems without spherical symmetry, and use this model to interpret new
fluorescence measurements on these plasmas. By assuming a self-similar
expansion, it is possible to solve the fluid equations analytically and to
include velocity effects to predict the fluorescence signals. In spite of the
simplicity of this approach, the model reproduces the major features of the
experimental data
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SLS Processing Studies of Nylon 11 Nanocomposites
Selective Laser Sintering (SLS) is widely used for rapid prototyping/manufacturing of
nylon 11 and nylon 12 parts. This processing technique has not been explored for
nylon nanocomposites. This study investigates the technicalities of processing nylon
11-clay and nylon-carbon nanofiber nanocomposites with SLS. Microstructural
analyses of the SLS powders and parts were conducted under SEM. Results suggest
that SLS processing is possible with the new nylon 11 nanocomposites. Yet the SLS
parts built have inferior properties relative to those of injection molding, suggesting
that more fine tuning for the processing is required.Mechanical Engineerin
Modelling crystal aggregation and deposition\ud in the catheterised lower urinary tract
Urethral catheters often become encrusted with crystals of magnesium struvite and calcium phosphate. The encrustation can block the catheter, which can cause urine retention in the bladder and reflux into the kidneys. We develop a mathematical model to investigate crystal deposition on the catheter surface, modelling the bladder as a reservoir of fluid and the urethral catheter as a rigid channel. At a constant rate, fluid containing crystal particles of unit size enters the reservoir, and flows from the reservoir through the channel and out of the system. The crystal particles aggregate, which we model using Becker–Döring coagulation theory, and are advected through the channel, where they continue to aggregate and are deposited on the channel’s walls. Inhibitor particles also enter the reservoir, and can bind to the crystals, preventing further aggregation and deposition. The crystal concentrations are spatially homogeneous in the reservoir, whereas the channel concentrations vary spatially as a result of advection, diffusion and deposition. We investigate the effect of inhibitor particles on the amount of deposition. For all parameter values, we find that crystals deposit along the full length of the channel, with maximum deposition close to the channel’s entrance
Fluorescence measurements of expanding strongly-coupled neutral plasmas
We report new detailed density profile measurements in expanding
strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques,
we determine plasma densities in the range of 10^5 to 10^9/cm^3 with a time
resolution limit as small as 7 ns. Strong-coupling in the plasma ions is
inferred directly from the fluorescence signals. Evidence for strong-coupling
at late times is presented, confirming a recent theoretical result.Comment: submitted to PR
Analytical model of non-Markovian decoherence in donor-based charge quantum bits
We develop an analytical model for describing the dynamics of a donor-based
charge quantum bit (qubit). As a result, the quantum decoherence of the qubit
is analytically obtained and shown to reveal non-Markovian features: The
decoherence rate varies with time and even attains negative values, generating
a non-exponential decay of the electronic coherence and a later recoherence.
The resulting coherence time is inversely proportional to the temperature, thus
leading to low decoherence below a material dependent characteristic
temperature.Comment: 19 pages, 3 figure
Solar modulation and interplanetary gradients of the galactic electrons flux, 1977 - 1984
The flux of electrons with energy from approx. 10 to 180 MeV measured with the electron telescope on the Voyager 1 and 2 spacecraft in the heliocentric radial range 1 - 22 AU between 1977 and 1984 is reported. Jovian electrons were clearly observable between 1978 and 1983 (radial range 2 - 12 AU) at energies below approx. 50 MeV. Above approx. 50 MeV the electron intensity exhibited temporal variations generally related to the 11 year modulation of protons 75 MeV. The overall magnitude of the electron intensity changes between the maximum intensity observed in 1977 and the minimum intensity in 1981 was a factor approx. 2, also comparable to that observed for 75 MeV protons. By early 1985 the electron intensity had apparently recovered to the level observed in 1977 whereas the proton intensity was still about 20% lower. A detailed interpretation of these electron variations in all energy channels depends on an accurate subtraction of background induced by energetic protons of a few 100 MeV. This subtraction is facilitated by calibration results at several energies
Decision Support Design for Workload Mitigation in Human Supervisory Control of Multiple Unmanned Aerial Vehicles
As UAVs become increasingly autonomous, the multiple personnel currently required to operate
a single UAV may eventually be superseded by a single operator concurrently managing
multiple UAVs. Instead of lower-level tasks performed by today’s UAV teams, the sole operator
would focus on high-level supervisory control tasks such as monitoring mission timelines and
reacting to emergent mission events. A key challenge in the design of such single-operator
systems will be the need to minimize periods of excessive workload that could arise when
critical tasks for several UAVs occur simultaneously. To a certain degree, it is possible to predict
and mitigate such periods in advance. However, actions that mitigate a particular period of high
workload in the short term may create long term episodes of high workload that were previously
non-existent. Thus some kind of decision support is needed that facilitates an operator’s ability to
evaluate different options for managing a mission schedule in real-time.
This paper describes two decision support visualizations designed for supervisory control of four
UAVs performing a time-critical targeting mission. A configural display common to both
visualizations, named the StarVis, was designed to highlight potential periods of high workload
corresponding to the current mission timeline, as well as “what if” projections of possible high
workload periods based upon different operator options. The first visualization design allows an
operator to compare different high workload mitigation options for individual UAVs. This is
termed the local visualization. The second visualization is indicates the combined effects of
multiple high workload mitigation decisions on the timeline. This is termed the global
visualization. The main advantage of the local visualization is that options can be compared
directly; however, the possible effects of these options on the mission timeline are only indicated
for the individual UAV primarily affected by the decision. For the global visualization, different
decisions can be combined to show possible effects on the system propagated across all UAVs,
but the different alternatives of a single decision option alternative cannot be directly compared.
An experiment was conducted testing these visualizations against a control with no visualization.
Results showed that subject using the local visualization had better performance, higher
situational awareness, and no significant increase in workload over the other two experimental
conditions. This occurred despite the fact that the local and global StarVis displays were very
similar. Not only did the Global StarVis produce degraded results as compared to the local
StarVis, but those participants with no visualization performed as well as those with the global
StarVis. This disparity in performance despite strong visual similarities in the StarVis designs is
attributed to operators’ inability to process all the information presented in the global StarVis as
well as the fact that participants with the local StarVis were able to rapidly develop effective
cognitive problem strategies. This research effort highlights a very important design
consideration, in that a single decision support design can produce very different performance
results when applied at different levels of abstraction.Prepared for Kevin Burns, The MITRE Corporatio
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