14,915 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
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
Asymptotic solutions of glass temperature profiles during steady optical fibre drawing
In this paper we derive realistic simplified models for the high-speed drawing of glass optical fibres via the downdraw method, that capture the fluid dynamics and heat transport in the fibre via conduction, convection and radiative heating. We exploit the small aspect ratio of the fibre and the relative orders of magnitude of the dimensionless parameters that characterize the heat transfer to reduce the problem to one- or two-dimensional systems via asymptotic analysis. The resulting equations may be readily solved numerically and in many cases admit exact analytic solutions. The systematic asymptotic breakdown presented is used to elucidate the relative importance of furnace temperature profile, convection, surface radiation and conduction in each portion of the furnace and the role of each in controlling the glass temperature.\ud
\ud
The models derived predict many of the qualitative features observed in the real industrial process, such as the glass temperature profile within the furnace and the sharp transition in fibre thickness. The models thus offer a desirable route to quick scenario testing, providing valuable practical information into the dependencies of the solution on the parameters and the dominant heat-transport mechanism
Operator Scheduling Strategies in Supervisory Control of Multiple UAVs
The application of network centric operations to time-constrained command and control environments
will mean that human operators will be increasingly responsible for multiple simultaneous supervisory
control tasks. One such futuristic application will be the control of multiple unmanned aerial vehicles
(UAVs) by a single operator. To achieve such performance in complex, time critical, and high risk
settings, automated systems will be required both to guarantee rapid system response as well as
manageable workload for operators. Through the development of a simulation test bed for human
supervisory control of multiple independent UAVs by a single operator, this paper presents recent
efforts to investigate workload mitigation strategies as a function of increasing automation. A humanin-
the-loop experiment revealed that under low workload conditions, operators’ cognitive strategies
were relatively robust across increasing levels of automated decision support. However, when
provided with explicit automated recommendations and with the ability to negotiate with external
agencies for delays in arrival times for targets, operators inappropriately fixated on the need to globally
optimize their schedules. In addition, without explicit visual representation of uncertainty, operators
tended to treated all probabilities uniformly. This study also revealed that operators that reached
cognitive saturation adapted two very distinct management strategies, which led to varying degrees of
success. Lastly, operators with management-by-exception decision support exhibited evidence of
automation bias.This research was sponsored by Boeing Phantom Works
A Predictive Model for Human-Unmanned Vehicle Systems : Final Report
Advances in automation are making it possible for a single operator to control multiple unmanned
vehicles (UVs). This capability is desirable in order to reduce the operational costs of human-UV systems
(HUVS), extend human capabilities, and improve system effectiveness. However, the high complexity
of these systems introduces many significant challenges to system designers. To help understand and
overcome these challenges, high-fidelity computational models of the HUVS must be developed. These
models should have two capabilities. First, they must be able to describe the behavior of the various
entities in the team, including both the human operator and the UVs in the team. Second, these models
must have the ability to predict how changes in the HUVS and its mission will alter the performance
characteristics of the system. In this report, we describe our work toward developing such a model. Via
user studies, we show that our model has the ability to describe the behavior of a HUVS consisting of a
single human operator and multiple independent UVs with homogeneous capabilities. We also evaluate
the model’s ability to predict how changes in the team size, the human-UV interface, the UV’s autonomy
levels, and operator strategies affect the system’s performance.Prepared for MIT Lincoln Laborator
Identifying Predictive Metrics for Supervisory Control of Multiple Robots
In recent years, much research has focused on making possible single operator control of multiple robots. In these high workload situations, many questions arise including how many robots should be in the team, which autonomy levels should they employ, and when should these autonomy levels
change? To answer these questions, sets of metric classes should be identified that capture these aspects of the human-robot team. Such a set of metric classes should have three properties. First, it should contain the key performance parameters of the system. Second, it should identify the limitations of the agents in the system. Third, it should have predictive power. In this paper, we decompose a human-robot team consisting of a single human and multiple robots in an effort to identify such a set of metric classes.
We assess the ability of this set of metric classes to (a) predict the number of robots that should be in the team and (b) predict system effectiveness. We do so by comparing predictions with actual data from a user study, which is also described.This research was funded by MIT Lincoln Laboratory
Susans Career Dilemma At MGR, LLC
Professionals starting their first job after graduate school want to launch a successful career. Unfortunately, some of them soon find out that performing at a high level does not always guarantee rapid promotion or success in their organization. This is a story about Susan, a highly recruited attorney, who joined an established law firm in Washington, DC, and was slow to realize that managing her boss is a critical skill needed for her survival and prosperity. Carlos, her direct supervisor and advocate of a tough love approach to management, views the effective nurturance and mentoring of new employees as his means of entr into the ranks of senior partner. Carlos and Susan are on a collision course with a potential impact on both of their careers. Susan needed to decide at the end of the case what to do to strategically manage her career
Recommended from our members
Durvalumab: an investigational anti-PD-L1 monoclonal antibody for the treatment of urothelial carcinoma.
Our expanding knowledge of immunotherapy for solid tumors has led to an explosion of clinical trials aimed at urothelial carcinoma. The primary strategy is centered on unleashing the immune system by releasing the inhibitory signals propagated by programmed cell death-1 (PD-1) and its ligand programmed cell death ligand-1 (PD-L1). Many antibody constructs have been developed to block these interactions and are used in clinical trials. The Food and Drug Administration has already approved a number of checkpoint inhibitors such as anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA4) monoclonal antibodies including ipilimumab; anti-PD-1 monoclonal antibodies including nivolumab and pembrolizumab; anti-PD-L1 antibodies including atezolizumab, avelumab, and durvalumab. One of the latest inhibitors is durvalumab, which is a high-affinity human immunoglobulin G1 kappa monoclonal antibody and blocks the interaction of PD-L1 with PD-1 and CD80. Currently, there are a number of ongoing trials in advanced urothelial carcinoma both using durvalumab monotherapy and in combination with other targeted therapies. In addition, durvalumab is being investigated in the non-muscle-invasive urothelial carcinoma, which is centered around intravenous formulations. These exciting developments have added a significant number of therapies in a previously limited treatment landscape
- …