12,886 research outputs found
On the evolution of non-axisymmetric viscous fibres with surface tension, inertia and gravity
We consider the free boundary problem for the evolution of a nearly straight slender fibre of viscous fluid. The motion is driven by prescribing the velocity of the ends of the fibre, and the free surface evolves under the action of surface tension, inertia and gravity. The three-dimensional Navier-Stokes equations and free-surface boundary conditions are analysed asymptotically, using the fact that the inverse aspect ratio, defined to be the ratio between a typical fibre radius and the initial fibre length, is small. This first part of the paper follows earlier work on the stretching of a slender viscous fibre with negligible surface tension effects. The inclusion of surface tension seriously complicates the problem for the evolution of the shape of the cross-section. We adapt ideas applied previously to two-dimensional Stokes flow to show that the shape of the cross-section can be described by means of a conformal map which depends on time and distance along the fibre axis. We give some examples of suitable relevant maps and present numerical solutions of the resulting equations. We also use analytic methods to examine the coupling between stretching and the evolution of the cross-section shape
Geosciences for Elementary Educators: A Course Assessment
Geosciences for Elementary Educators engages future elementary teachers in a hands-on investigation of topics aligned with the third and fifth grade Earth/Space Science and Scientific Inquiry benchmarks of the Oregon Content Standards. The course was designed to develop the content background of elementary teachers within the framework of the science described in the content standards, to provide an opportunity for future teachers to explore the content area in relation to what takes place in the classrooms of elementary schools, and to initiate a community of learners focused on teaching science to elementary students. The course focused on four themes: the classroom teacher as an activity and curriculum developer using diverse resources to keep the content current and alive; the classroom teacher as educator dealing with the diverse backgrounds of students in a developmentally appropriate manner; the classroom teacher as reflective practitioner exploring the links among pedagogy, content, and student learning; and, the classroom teacher as citizen staying current with emerging policy issues and debates that impact education. In a course where process is extremely important, participants are assessed on what they can do with content and process knowledge through preparing lesson plans, presenting lessons in a simulated classroom environment, and developing a portfolio and journal. Lesson plans demonstrate participant understanding of inquiry, using models, deductive and inductive approaches, links between communication skills and content knowledge, and effective use of technology, including the Internet. For each topic, the mixture of demonstration, experimentation, inquiry, and lecture models are explored through investigation, discovery, and analysis
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
Assessing the Impact of Auditory Peripheral Displays for UAV Operators
A future implementation of unmanned aerial vehicle (UAV) operations is having a single
operator control multiple UAVs. The research presented here explores possible avenues of
enhancing audio cues of UAV interfaces for this futuristic control of multiple UAVs by a single
operator. This project specifically evaluates the value of continuous and discrete audio cues as
indicators of course deviations or late arrivals to targets for UAV missions. It also looks at the
value of the audio cues in single and multiple UAV scenarios.
To this end, an experiment was carried out on the Multiple Autonomous Unmanned Vehicle
Experimental (MAUVE) test bed developed in the Humans and Automation Laboratory at the
Massachusetts Institute of Technology with 44 military participants. Specifically, two continuous
audio alerts were mapped to two human supervisory tasks within MAUVE. One of the
continuous audio alerts, an oscillating course deviation alert was mapped to UAV course
deviations which occurred over a continual scale. The other continuous audio alert tested was a
modulated late arrival alert which alerted the operator when a UAV was going to be late to a
target. In this case the continuous audio was mapped to a discrete event in that the UAV was
either on time or late to a target. The audio was continuous in that it was continually on and
alerting the participant to the current state of the UAV. It either was playing a tone indicating
the UAV was on time to a target or playing a tone indicating the UAV was late to a target. These
continuous alerts were tested against more traditional single beep alerts which acted as discrete
alerts. The beeps were discrete in that when they were used for monitoring course deviations a
single beep was played when the UAV got to specific threshold off of the course or for late
arrivals a single beep was played when the UAV became late.
The results show that the use of the continuous audio alerts enhances a single operator’s
performance in monitoring single and multiple semi-autonomous vehicles. However, the results
also emphasize the necessity to properly integrate the continuous audio with the other auditory
alarms and visual representations in a display, as it is possible for discrete audio alerts to be lost
in aural saliency of continuous audio, leaving operators reliant on the visual aspects of the
display.Prepared for Charles River Analytics, Inc
An Experimental Platform for Investigating Decision and Collaboration Technologies in Time-Sensitive Mission Control Operations
This report describes the conceptual design and detailed architecture of an experimental platform
developed to support investigations of novel decision and collaboration technologies for
complex, time-critical mission control operations, such as military command and control and
emergency response. In particular, the experimental platform is designed to enable exploration
of novel interface and interaction mechanisms to support both human-human collaboration and
human-machine collaboration for mission control operations involving teams of human operators
engaged in supervisory control of intelligent systems, such as unmanned aerial vehicles (UAVs).
Further, the experimental platform is designed to enable both co-located and distributed
collaboration among operations team members, as well as between team members and relevant
mission stakeholders.
To enable initial investigations of new information visualization, data fusion, and data sharing
methods, the experimental platform provides a synthetic task environment for a representative
collaborative time-critical mission control task scenario. This task scenario involves a UAV
operations team engaged in intelligence, surveillance, and reconnaissance (ISR) activities. In the
experimental task scenario, the UAV team consists of one mission commander and three
operators controlling multiple, homogeneous, semi-autonomous UAVs. In order to complete its
assigned missions, the UAV team must coordinate with a ground convoy, an external strike
team, and a local joint surveillance and target attack radar system (JSTARS). This report details
this task scenario, including the possible simulation events that can occur and the logic
governing the simulation dynamics.
In order to perform human-in-the-loop experimentation within the synthetic task environment,
the experimental platform also consists of a physical laboratory designed to emulate a miniature
command center. The Command Center Laboratory comprises a number of large-screen
displays, multi-screen operator stations, and mobile, tablet-style devices. This report details the
physical configuration and hardware components of this Command Center Laboratory. Details
are also provided of the software architecture used to implement the synthetic task environment
and experimental interface technologies to facilitate user experiments in this laboratory.
The report also summarizes the process of conducting an experiment in the experimental
platform, including details of scenario design, hardware and software instrumentation, and
participant training. Finally, the report suggests several improvements that could be made to the
experimental platform based on insights gained from initial user experiments that have been
conducted in this environment.Prepared For Boeing, Phantom Work
Cognitive Task Analysis for the LCS Operator
In support of Plan Understanding for Mixed-initiative control of Autonomous systems (PUMA)The following Tables and Figures detail the cognitive task analysis (CTA) performed to
determine the information requirements needed to support a single operator located aboard the
futuristic Littoral Combat Ship (LCS). This operator is responsible for controlling four
underwater unmanned vehicles in conjunction with a UAV operating on a shared network.
• Table 1 is a scenario task overview that breaks the overall mission into 3 phases
(planning, execution, and recovery) and then details the subtasks for each of the 3
mission phases.
• Figure 1 is an event flow diagram that demonstrates what events must occur in a temporal
order for each of the 3 phases. There are three basic event types in Figure 1: 1) a loop (L)
that represents a process that occurs in a looping fashion until some predetermined event
occurs, 2) a decision (D) that represents some decision that is required from the LCS
operator, and 3) a process (P) which requires some human-computer interaction to
support the required tasks. In each event block, an alphanumeric code is included which
labels that particular event type (L#, D#, P#). This label is important because later
information requirements will be mapped to one of these events.
• Table 2, which details the situation awareness (SA) requirements for the LCS Operator
for each of the 3 mission phases and associated subtasks. Each of these SA requirements
is mapped directly to one or more events in Figure 1.
Because the decisions in Figure 1 represent critical events that require detailed understanding of
what information and knowledge is needed to support the operator’s decision-making process,
decision ladders were constructed for the diamonds and loops in Figure 1 that correspond to an
involved decision process to resolve the question being posed at that stage in the event flow
(Figures 2-4). Decision ladders are modeling tools that capture the states of knowledge and
information-processing activities necessary to reach a decision. Decision ladders can help
identify the information that either the automation and/or the human will need to perform or
monitor a task. Decision Ladders, illustrate the need not only for the same information identified
by the cognitive task analysis, but the need for several other pieces of information such as the
need for visual or aural alerts in contingency situations. In Figures 2-4, three versions are
included that detail (a) the basic decision ladder, (b) the decision ladder with corresponding
display requirements, and (c) the decision ladder with possible levels of automation.
• Figure 2 represents the automated target recognition (ATR) decision ladder (D3 from
Event Flow): (a) decision ladder, (b) decision ladder with corresponding display
requirements, and (c) decision ladder with possible levels of automation.
• Figure 3 shows the decision ladder information and knowledge requirements for the
sentry handoff (L3 from Event Flow).
• Figure 4, the UUV Recovery Decision Ladder (D7 from Event Flow), illustrates what
information is nominally needed. Since this phase was not a major focus, the decision
ladder is not as detailed as it could be. This should be a point of focus in Phase II.
Lastly Figure 5 demonstrates the coordination loop that must occur in the case where a handoff
failure occurs (for a number of reasons to include equipment failure, communication delays, etc.)
Again, because the multi-player coordination issues are not a primary focus in Phase I but are a
significant consideration for any follow-on phases.Prepared for Charles River Analytic
Assessing the Impact of Haptic Peripheral Displays for UAV Operators
Objectives: A pilot study was conducted to investigate the effectiveness of continuous haptic
peripheral displays in supporting multiple UAV supervisory control. Background: Previous
research shows that continuous auditory peripheral displays can enhance operator performance in
monitoring events that are continuous in nature, such as monitoring how well UAVs stay on their
pre-planned courses. This research also shows that auditory alerts can be masked by other
auditory information. Command and control operations are generally performed in noisy
environments with multiple auditory alerts presented to the operators. In order to avoid this
masking problem, another potentially useful sensory channel for providing redundant
information to UAV operators is the haptic channel. Method: A pilot experiment was conducted
with 13 participants, using a simulated multiple UAV supervisory control task. All participants
completed two haptic feedback conditions (continuous and threshold), where they received alerts
based on UAV course deviations and late arrivals to targets. Results: Threshold haptic feedback
was found to be more effective for late target arrivals, whereas continuous haptic feedback
resulted in faster reactions to course deviations. Conclusions: Continuous haptic feedback
appears to be more appropriate for monitoring events that are continuous in nature (i.e., how well
a UAV keeps its course). In contrast, threshold haptic feedback appears to better support
response to discrete events (i.e., late target arrivals). Future research: Because this is a pilot
study, more research is needed to validate these preliminary findings. A direct comparison
between auditory and haptic feedback is also needed to provide better insights into the potential
benefits of multi-modal peripheral displays in command and control of multiple UAVs.Prepared for Charles River Analytics, Inc
Assisting Interruption Recovery in Mission Control Operations
Frequent interruptions are commonplace in modern work environments. The negative
impacts of interruptions are well documented and include increased task completion and
error rates in individual task activities, as well as interference with team coordination in
team-based activities. The ramifications of an interruption in mission control operations,
such as military command and control and emergency response, can be particularly costly
due to the time and life-critical nature of these operations. The negative impacts of
interruptions have motivated recent developments in software tools, called interruption
recovery tools, which help mitigate the effects of interruptions in a variety of task
environments. However, mission control operations introduce particular challenges for
the design of these tools due to the dynamic and highly collaborative nature of these
environments.
To address this issue, this report investigates methods of reducing the negative
consequences of interruptions in complex, mission control operations. In particular, this
report focuses on supporting interruption recovery for team supervisors in these
environments, as the research has shown that supervisors are particularly susceptible to
frequent interruptions. Based on the results of a requirements analysis, which involved a
cognitive task analysis of a representative mission control task scenario, a new
interruption recovery tool, named the Interruption Recovery Assistance (IRA) tool, was
developed. In particular, the IRA tool was designed to support a military mission
commander overseeing a team of unmanned aerial vehicle (UAV) operators performing
ground force protection operations. The IRA tool provides the mission commander a
visual summary of mission changes, in the form of an event bookmark timeline. It also
provides interactive capabilities to enable the commander to view additional information
on the primary task displays when further detail about a particular mission event is
needed.
The report also presents the findings from a user study that was conducted to evaluate the
effectiveness of the IRA tool on interruption recovery during collaborative UAV mission
operations. The study produced mixed results regarding the effectiveness of the IRA tool.
The statistical analysis indicated a negative impact on recovery time, while indicating a
positive impact on decision accuracy, especially in complex task situations. The study
also indicated that the effect of the IRA tool varied across differ user populations. In
particular, the IRA tool tended to provide greater benefits to participants without military
experience, compared to military participants involved in the study. The qualitative
findings from the study provided key insights into the impact and utility of the IRA tool.
These insights were used to identify several future research and design directions related
to interruption recovery in mission control operations.Prepared for Boeing Phantom Work
The Impact of Intelligent Aiding for Multiple Unmanned Aerial Vehicle Schedule Management
There is increasing interest in designing systems such that the current many-to-one ratio of operators to unmanned vehicles (UVs) can be inverted. Instead of lower-level tasks performed by today’s UV teams, the sole operator would focus on high-level supervisory control tasks. A key challenge in the design of such single-operator systems will be the need to minimize periods of excessive workload that arise when critical tasks for several UVs occur simultaneously. Thus some kind of decision support is needed that facilitates an operator’s ability to evaluate different action alternatives for managing a multiple UV mission schedule in real-time. This paper describes two decision support experiments that attempted to provide UAV operators with multivariate scheduling assistance, with mixed results. Those automated decision support tools that provided more local, as opposed to global, visual recommendations produced superior performance, suggesting that meta-information displays could saturate operators and reduce performance.This research was sponsored by Boeing Phantom Work and Mitre, Inc
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