15,906 research outputs found
On-board timeline validation and repair : a feasibility study
We report on the progress and outcome of a recent ESAfunded project (MMOPS) designed to explore the feasibility of on-board reasoning about payload timelines. The project sought to examine the role of on-board timeline reasoning and the operational context into which it would fit. We framed a specification for an on-board service that fits with existing practices and represents a plausible advance within sensible constraints on the progress of operations planning. We have implemented a prototype to demonstrate the feasibility of such a system and have used it to show how science gathering operations might be improved by its deployment
A review of modular strategies and architecture within manufacturing operations
This paper reviews existing modularity and modularization literature within manufacturing operations. Its purpose is to examine the tools, techniques, and concepts relating to modular production, to draw together key issues currently dominating the literature, to assess managerial implications associated with the emerging modular paradigm, and to present an agenda for future research directions. The review is based on journal papers included in the ABI/Inform electronic database and other noteworthy research published as part of significant research programmes. The research methodology concerns reviewing existing literature to identify key modular concepts, to determine modular developments, and to present a review of significant contributions to the field. The findings indicate that the modular paradigm is being adopted in a number of manufacturing organizations. As a result a range of conceptual tools, techniques, and frameworks has emerged and the field of modular enquiry is in the process of codifying the modular lexicon and developing appropriate modular strategies commensurate with the needs of manufacturers. Modular strategies and modular architecture were identified as two key issues currently dominating the modular landscape. Based on this review, the present authors suggest that future research areas need to focus on the development and subsequent standardization of interface protocols, cross-brand module use, supply chain power, transparency, and trust. This is the first review of the modular landscape and as such provides insights into, first, the development of modularization and, second, issues relating to designing modular products and modular supply chains
Anisotropic Fermi Contour of (001) GaAs Holes in Parallel Magnetic Fields
We report a severe, spin-dependent, Fermi contour anisotropy induced by
parallel magnetic field in a high-mobility (001) GaAs two-dimensional hole
system. Employing commensurability oscillations created by a unidirectional,
surface-strain-induced, periodic potential modulation, we directly probe the
anisotropy of the two spin subband Fermi contours. Their areas are obtained
from the Fourier transform of the Shubnikov-de Haas oscillations. Our findings
are in semi-quantitative agreement with the results of parameter-free
calculations of the energy bands.Comment: 4 pages, 4 figure
Anisotropic composite fermions and fractional quantum Hall effect
We study the role of anisotropy on the transport properties of composite
fermions near Landau level filling factor in two-dimensional holes
confined to a GaAs quantum well. By applying a parallel magnetic field, we tune
the composite fermion Fermi sea anisotropy and monitor the relative change of
the transport scattering time at along the principal directions.
Interpreted in a simple Drude model, our results suggest that the scattering
time is longer along the longitudinal direction of the composite fermion Fermi
sea. Furthermore, the measured energy gap for the fractional quantum Hall state
at decreases when anisotropy becomes significant. The decrease,
however, might partly stem from the charge distribution becoming bilayer-like
at very large parallel magnetic fields
Anisotropic Fermi Contour of (001) GaAs Electrons in Parallel Magnetic Fields
We demonstrate a severe Fermi contour anisotropy induced by the application
of a parallel magnetic field to high-mobility electrons confined to a
30-nm-wide (001) GaAs quantum well. We study commensurability oscillations,
namely geometrical resonances of the electron orbits with a unidirectional,
surface-strain-induced, periodic potential modulation, to directly probe the
size of the Fermi contours along and perpendicular to the parallel field. Their
areas are obtained from the Shubnikov-de Haas oscillations. Our experimental
data agree semi-quantitatively with the results of parameter-free calculations
of the Fermi contours but there are significant discrepancies.Comment: 5 pages, 5 figure
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