88,212 research outputs found
Physiological assessment of operator workload during manual tracking. 1: Pupillary responses
The feasibility of pupillometry as an indicator for assessing operator workload during manual tracking was studied. The mean and maximum pupillary responses of 12 subjects performing tracking tasks with three levels of difficulty (bandwidth of the forcing function were 0.15, 0.30 and 0.50 Hz respectively) were analysed. The results showed that pupillary dilation increased significantly as a function of the tracking difficulty which was reflected by the significant increase of tracking error (RMS). The present study supplies additional evidence that pupillary response is a sensitive and reliable index which may serve as an indicator for assessing operator workload in man-machine systems
Impacts of Fire Emissions and Transport Pathways on the Interannual Variation of CO In the Tropical Upper Troposphere
This study investigates the impacts of fire emission, convection, various climate conditions and transport pathways on the interannual variation of carbon monoxide (CO) in the tropical upper troposphere (UT), by evaluating the field correlation between these fields using multi-satellite observations and principle component analysis, and the transport pathway auto-identification method developed in our previous study. The rotated empirical orthogonal function (REOF) and singular value decomposition (SVD) methods are used to identify the dominant modes of CO interannual variation in the tropical UT and to study the coupled relationship between UT CO and its governing factors. Both REOF and SVD results confirm that Indonesia is the most significant land region that affects the interannual variation of CO in the tropical UT, and El Nino-Southern Oscillation (ENSO) is the dominant climate condition that affects the relationships between surface CO emission, convection and UT CO. In addition, our results also show that the impact of El Nino on the anomalous CO pattern in the tropical UT varies strongly, primarily due to different anomalous emission and convection patterns associated with different El Nino events. In contrast, the anomalous CO pattern in the tropical UT during La Nina period appears to be less variable among different events. Transport pathway analysis suggests that the average CO transported by the "local convection" pathway (Delta COlocal) accounts for the differences of UT CO between different ENSO phases over the tropical continents during biomass burning season. Delta COlocal is generally higher over Indonesia-Australia and lower over South America during El Nino years than during La Nina years. The other pathway ("advection within the lower troposphere followed by convective vertical transport") occurs more frequently over the west-central Pacific during El Nino years than during La Nina years, which may account for the UT CO differences over this region between different ENSO phases.NASA Aura Science Team (AST) program NNX09AD85GJackson School of Geosciences at the University of Texas at AustinJet Propulsion Laboratory, California Institute of Technology, under NASAGeological Science
Thermodynamic properties and phase diagrams of spin-1 quantum Ising systems with three-spin interactions
The spin-1 quantum Ising systems with three-spin interactions on
two-dimensional triangular lattices are studied by mean-field method. The
thermal variations of order parameters and phase diagrams are investigated in
detail. The stable, metastable and unstable branches of the order parameters
are obtained. According to the stable conditions at critical point, we find
that the systems exhibit tricritical points. With crystal field and biquadratic
interactions, the system has rich phase diagrams with single reentrant or
double reentrant phase transitions for appropriate ranges of the both
parameters.Comment: 10 pages, 5 figure
MHD Simulation of the Inner-Heliospheric Magnetic Field
Maps of the radial magnetic field at a heliocentric distance of ten solar
radii are used as boundary conditions in the MHD code CRONOS to simulate a 3D
inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The
input data for the magnetic field are the result of solar surface flux
transport modelling using observational data of sunspot groups coupled with a
current sheet source surface model. Amongst several advancements, this allows
for higher angular resolution than that of comparable observational data from
synoptic magnetograms. The required initial conditions for the other MHD
quantities are obtained following an empirical approach using an inverse
relation between flux tube expansion and radial solar wind speed. The
computations are performed for representative solar minimum and maximum
conditions, and the corresponding state of the solar wind up to the Earths
orbit is obtained. After a successful comparison of the latter with
observational data, they can be used to drive outer-heliospheric models.Comment: for associated wmv movie files accompanying Figure 7, see
http://www.tp4.rub.de/~tow/max.wmv and http://www.tp4.rub.de/~tow/min.wm
Surface flux transport modeling for solar cycles 15--21: effects of cycle-dependent tilt angles of sunspot groups
We model the surface magnetic field and open flux of the Sun from 1913 to
1986 using a surface flux transport model, which includes the observed
cycle-to-cycle variation of sunspot group tilts. The model reproduces the
empirically derived time evolution of the solar open magnetic flux, and the
reversal times of the polar fields. We find that both the polar field and the
axial dipole moment resulting from this model around cycle minimum correlate
with the strength of the following cycle.Comment: Accepted for publication by Ap
Solar activity forecast with a dynamo model
Although systematic measurements of the solar polar magnetic field exist only
from mid 1970s, other proxies can be used to infer the polar field at earlier
times. The observational data indicate a strong correlation between the polar
field at a sunspot minimum and the strength of the next cycle, although the
strength of the cycle is not correlated well with the polar field produced at
its end. This suggests that the Babcock Leighton mechanism of poloidal field
generation from decaying sunspots involves randomness, whereas the other
aspects of the dynamo process must be reasonably ordered and deterministic.
Only if the magnetic diffusivity within the convection zone is assumed to be
high, we can explain the correlation between the polar field at a minimum and
the next cycle. We give several independent arguments that the diffusivity must
be of this order. In a dynamo model with diffusivity like this, the poloidal
field generated at the mid latitudes is advected toward the poles by the
meridional circulation and simultaneously diffuses towards the tachocline,
where the toroidal field for the next cycle is produced. To model actual solar
cycles with a dynamo model having such high diffusivity, we have to feed the
observational data of the poloidal field at the minimum into the theoretical
model. We develop a method of doing this in a systematic way. Our model
predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of
solar activity is also calculated with our model and compared with
observational data.Comment: 17 pages, 18 figures, submitted to MNRA
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