7,704 research outputs found
POPEYE: A production rule-based model of multitask supervisory control (POPCORN)
Recent studies of relationships between subjective ratings of mental workload, performance, and human operator and task characteristics have indicated that these relationships are quite complex. In order to study the various relationships and place subjective mental workload within a theoretical framework, we developed a production system model for the performance component of the complex supervisory task called POPCORN. The production system model is represented by a hierarchial structure of goals and subgoals, and the information flow is controlled by a set of condition-action rules. The implementation of this production system, called POPEYE, generates computer simulated data under different task difficulty conditions which are comparable to those of human operators performing the task. This model is the performance aspect of an overall dynamic psychological model which we are developing to examine and quantify relationships between performance and psychological aspects in a complex environment
Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
We present 2D MHD simulations of the radiatively driven outflow from a
rotating hot star with a dipole magnetic field aligned with the star's rotation
axis. We focus primarily on a model with moderately rapid rotation (half the
critical value), and also a large magnetic confinement parameter, . The magnetic field
channels and torques the wind outflow into an equatorial, rigidly rotating disk
extending from near the Kepler corotation radius outwards. Even with
fine-tuning at lower magnetic confinement, none of the MHD models produce a
stable Keplerian disk. Instead, material below the Kepler radius falls back on
to the stellar surface, while the strong centrifugal force on material beyond
the corotation escape radius stretches the magnetic loops outwards, leading to
episodic breakout of mass when the field reconnects. The associated dissipation
of magnetic energy heats material to temperatures of nearly K, high
enough to emit hard (several keV) X-rays. Such \emph{centrifugal mass ejection}
represents a novel mechanism for driving magnetic reconnection, and seems a
very promising basis for modeling X-ray flares recently observed in rotating
magnetic Bp stars like Ori E.Comment: 5 pages, 3 figures, accepted by ApJ
The most rapidly rotating He-strong emission line star: HR7355
Using archival spectroscopic and photometric data, we searched for massive
stars with Balmer-emission consistent with magnetically confined circumstellar
material. HR 7355 is a formerly unknown He-strong star showing Balmer emission.
At V=6.02 mag, it is one of the brightest objects simultaneously showing
anomalous helium absorption and hydrogen emission. Among similar objects, only
sigma Ori E has so far been subjected to any systematic analysis of the
circumstellar material responsible for the emission. We argue that the
double-wave photometric period of 0.52d corresponds to the rotation period. In
tandem with the high projected equatorial velocity, v sin i=320 km/s, this
short period suggests that HR 7355 is the most rapidly rotating He-strong star
known to date; a class that was hitherto expected to host stars with slow to
moderate rotation only.Comment: 4 pages with 2 figures. Accepted for publication as Research Note by
Astronomy and Astrophysic
A Bayesian approach for inferring the dynamics of partially observed endemic infectious diseases from space-time-genetic data
We describe a statistical framework for reconstructing the sequence of transmission events between observed cases of an endemic infectious disease using genetic, temporal and spatial information. Previous approaches to reconstructing transmission trees have assumed all infections in the study area originated from a single introduction and that a large fraction of cases were observed. There are as yet no approaches appropriate for endemic situations in which a disease is already well established in a host population and in which there may be multiple origins of infection, or that can enumerate unobserved infections missing from the sample. Our proposed framework addresses these shortcomings, enabling reconstruction of partially observed transmission trees and estimating the number of cases missing from the sample. Analyses of simulated datasets show the method to be accurate in identifying direct transmissions, while introductions and transmissions via one or more unsampled intermediate cases could be identified at high to moderate levels of case detection. When applied to partial genome sequences of rabies virus sampled from an endemic region of South Africa, our method reveals several distinct transmission cycles with little contact between them, and direct transmission over long distances suggesting significant anthropogenic influence in the movement of infected dogs
A Minimalist Turbulent Boundary Layer Model
We introduce an elementary model of a turbulent boundary layer over a flat
surface, given as a vertical random distribution of spanwise Lamb-Oseen vortex
configurations placed over a non-slip boundary condition line. We are able to
reproduce several important features of realistic flows, such as the viscous
and logarithmic boundary sublayers, and the general behavior of the first
statistical moments (turbulent intensity, skewness and flatness) of the
streamwise velocity fluctuations. As an application, we advance some heuristic
considerations on the boundary layer underlying kinematics that could be
associated with the phenomenon of drag reduction by polymers, finding a
suggestive support from its experimental signatures.Comment: 5 pages, 10 figure
The Thermodynamics of Kaluza-Klein Black Hole/Bubble Chains
A Killing bubble is a minimal surface that arises as the fixed surface of a
spacelike Killing field. We compute the bubble contributions to the Smarr
relations and the mass and tension first laws for spacetimes containing both
black holes and Killing bubbles. The resulting relations display an interesting
interchange symmetry between the properties of black hole horizons and those of
KK bubbles. This interchange symmetry reflects the underlying relation between
static bubbles and black holes under double analytic continuation of the time
and Kaluza-Klein directions. The thermodynamics of bubbles involve a
geometrical quantity that we call the bubble surface gravity, which we show has
several properties in common with the black hole surface gravity.Comment: 20 pages, 1 figur
- …