7,575 research outputs found
Generalized twistor spaces for hyperkähler manifolds
Let M be a hyperkaehler manifold. The S2-family of complex structures compatible with the hyperkaehler metric can be assembled into a single complex structure on Z = M × S2; the resulting complex manifold is known as the twistor space of M. We describe the analogous construction for generalized complex structures in the sense of Hitchin. Specifically, we exhibit a natural S2 × S2-family of generalized complex structures compatible with the hyperkaehler metric, and assemble them into a single generalized complex structure on X = M × S2 × S2. We call the resulting generalized complex manifold the generalized twistor space of M
Effects of digital altimetry on pilot workload
A series of VOR-DME instrument landing approaches was flown in the DC-9 full-workload simulator to compare pilot performance, scan behavior, and workload when using a computer-drum-pointer altimeter (CDPA) and a digital altimeter (DA). Six pilots executed two sets of instrument landing approaches, with a CDPA on one set and a DA on the other set. Pilot scanning parameters, flight performance, and subjective opinion data were evaluated. It is found that the processes of gathering information from the CDPA and the DA are different. The DA requires a higher mental workload than the CDPA for a VOR-DME type landing approach. Mental processing of altitude information after transitioning back to the attitude indicator is more evident with the DA than with the CDPA
Analytical techniques of pilot scanning behavior and their application
The state of the art of oculometric data analysis techniques and their applications in certain research areas such as pilot workload, information transfer provided by various display formats, crew role in automated systems, and pilot training are documented. These analytical techniques produce the following data: real-time viewing of the pilot's scanning behavior, average dwell times, dwell percentages, instrument transition paths, dwell histograms, and entropy rate measures. These types of data are discussed, and overviews of the experimental setup, data analysis techniques, and software are presented. A glossary of terms frequently used in pilot scanning behavior and a bibliography of reports on related research sponsored by NASA Langley Research Center are also presented
The Formation and Fragmentation of Disks around Primordial Protostars
The very first stars to form in the Universe heralded an end to the cosmic
dark ages and introduced new physical processes that shaped early cosmic
evolution. Until now, it was thought that these stars lived short, solitary
lives, with only one extremely massive star, or possibly a very wide binary
system, forming in each dark matter minihalo. Here we describe numerical
simulations that show that these stars were, to the contrary, often members of
tight multiple systems. Our results show that the disks that formed around the
first young stars were unstable to gravitational fragmentation, possibly
producing small binary and higher-order systems that had separations as small
as the distance between the Earth and the Sun.Comment: This manuscript has been accepted for publication in Science. This
version has not undergone final editing. Please refer to the complete version
of record at http://www.sciencemag.org
Open questions in the study of population III star formation
The first stars were key drivers of early cosmic evolution. We review the
main physical elements of the current consensus view, positing that the first
stars were predominantly very massive. We continue with a discussion of
important open questions that confront the standard model. Among them are
uncertainties in the atomic and molecular physics of the hydrogen and helium
gas, the multiplicity of stars that form in minihalos, and the possible
existence of two separate modes of metal-free star formation.Comment: 15 pages, 2 figures. To appear in the conference proceedings for IAU
Symposium 255: Low-Metallicity Star Formation: From the First Stars to Dwarf
Galaxie
Supporting novel home network management interfaces with Openflow and NOX
The Homework project has examined redesign of existing home network infrastructures to better support the needs and requirements of actual home users. Integrating results from several ethnographic studies, we have designed and built a home networking platform providing detailed per-flow measurement and management capabilities supporting several novel management interfaces. This demo specifically shows these new visualization and control interfaces, and describes the broader benefits of taking an integrated view of the networking infrastructure, realised through our router's augmented measurement and control APIs.
Aspects of this work have been published: the Homework Database in Internet Management (IM) 2011 and implications of the ethnographic results are to appear at the SIGCOMM W-MUST workshop 2011. Separate, more detailed expositions of the interface elements and system performance and implications are currently under submission at other venues. A partial code release is already available and we anticipate fuller public beta release by Q4 2011
A length scale for the superconducting Nernst signal above T in NbSi
We present a study of the Nernst effect in amorphous superconducting thin
films of NbSi. The field dependence of the Nernst coefficient
above T displays two distinct regimes separated by a field scale set by
the Ginzburg-Landau correlation length. A single function , with the
correlation length as its unique argument set either by the zero-field
correlation length (in the low magnetic field limit) or by the magnetic length
(in the opposite limit), describes the Nernst coefficient. We conclude that the
Nernst signal observed on a wide temperature () and field () range is exclusively generated by short-lived Cooper pairs.Comment: 4 pages, 4 figure
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