28,938 research outputs found
Detecting short periods of elevated workload. A compariÂson of nine workload assessment techniques
The present experiment tested the merits of 9 common workload assessment techniques with relatively short periods of workload in a car-driving task. Twelve participants drove an instrumented car and performed a visually loading task and a mentally loading task for 10, 30, and 60 s. The results show that 10-s periods of visual and mental workload can be measured successfully with subjective ratings and secondary task performance. With respect to longer loading periods (30 and 60 s), steering frequency was found to be sensitive to visual workload, and skin conductance response (SCR) was sensitive to mental workload. The results lead to preliminary guidelines that will help applied researchers to determine which techniques are best suited for assessing visual and mental workload
Formation of the binary pulsars J1141-6545 and B2023+46
The binaries PSR J1141-6545 and PSR B2303+46 each appear to contain a white
dwarf which formed before the neutron star. We describe an evolutionary pathway
to produce these two systems. In this scenario, the primary transfers its
envelope onto the secondary which is then the more massive of the two stars,
and indeed sufficiently massive later to produce a neutron star via a
supernova. The core of the primary produces a massive white dwarf which enters
into a common envelope with the core of the secondary when the latter evolves
off the main sequence. During the common envelope phase, the white dwarf and
the core of the secondary spiral together as the envelope is ejected. The
evolutionary history of PSR J1141-6545 and PSR B2303+46 differ after this
phase. In the case of PSR J1141--6545, the secondary (now a helium star)
evolves into contact transferring its envelope onto the white dwarf. We propose
that the vast majority of this material is in fact ejected from the system. The
remains of the secondary then explode as a supernova producing a neutron star.
Generally the white dwarf and neutron star will remain bound in tight, often
eccentric, systems resembling PSR J1141-6545. These systems will spiral in and
merge on a relatively short timescale and may make a significant contribution
to the population of gamma ray burst progenitors. In PSR B2303+46, the
helium-star secondary and white dwarf never come into contact. Rather the
helium star loses its envelope via a wind, which increases the binary
separation slightly. Only a small fraction of such systems will remain bound
when the neutron star is formed (as the systems are wider). Those systems which
are broken up will produce a population of high-velocity white dwarfs and
neutron stars.Comment: 9 pages, 10 figures; MNRAS in pres
The Origin of the Initial Mass Function
We review recent advances in our understanding of the origin of the initial
mass function (IMF). We emphasize the use of numerical simulations to
investigate how each physical process involved in star formation affects the
resulting IMF. We stress that it is insufficient to just reproduce the IMF, but
that any successful model needs to account for the many observed properties of
star forming regions including clustering, mass segregation and binarity.
Fragmentation involving the interplay of gravity, turbulence, and thermal
effects is probably responsible for setting the characteristic stellar mass.
Low-mass stars and brown dwarfs can form through the fragmentation of dense
filaments and disks, possibly followed by early ejection from these dense
environments which truncates their growth in mass. Higher-mass stars and the
Salpeter-like slope of the IMF are most likely formed through continued
accretion in a clustered environment. The effects of feedback and magnetic
fields on the origin of the IMF are still largely unclear. Lastly, we discuss a
number of outstanding problems that need to be addressed in order to develop a
complete theory for the origin of the IMF.Comment: PPV conference paper, 16 pages, 11 figur
Beam Misalignments and Fluid Velocities in Laser-Induced Thermal Acoustics
Beam misalignments and bulk fluid velocities can influence the time history and intensity of laser-induced thermal acoustics (LITA) signals. A closed-form analytic expression for LITA signals incorporating these effects is derived, allowing the magnitude of beam misalignment and velocity to be inferred from the signal shape. It is demonstrated how instantaneous, nonintrusive, and remote measurement of sound speed and velocity (Mach number) can be inferred simultaneously from homodyne-detected LITA signals. The effects of different forms of beam misalignment are explored experimentally and compared with theory, with good agreement, allowing the amount of misalignment to be measured from the LITA signal. This capability could be used to correct experimental misalignments and account for the effects of misalignment in other LITA measurements. It is shown that small beam misalignments have no influence on the accuracy or repeatability of sound speed measurements with LITA
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