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  • Lunar and Planetary Science and Exploration  (4)
  • Solar Physics  (2)
  • Key words. Assembly planning, Assembly sequencing, Motion space, Nondirectional blocking graph, Manufacturing.  (1)
  • Inorganic Chemistry
  • 2000-2004  (7)
Collection
Keywords
Publisher
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Year
  • 1
    Electronic Resource
    Electronic Resource
    A General Framework for Assembly Planning: The Motion Space Approach (2000)
    Springer
    Algorithmica 26 (2000), S. 577-601 
    Details
    ISSN: 1432-0541
    Keywords: Key words. Assembly planning, Assembly sequencing, Motion space, Nondirectional blocking graph, Manufacturing.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. Assembly planning is the problem of finding a sequence of motions to assemble a product from its parts. We present a general framework for finding assembly motions based on the concept of motion space . Assembly motions are parameterized such that each point in motion space represents a mating motion that is independent of the moving part set. For each motion we derive blocking relations that explicitly state which parts collide with other parts; each subassembly (rigid subset of parts) that does not collide with the rest of the assembly can easily be derived from the blocking relations. Motion space is partitioned into an arrangement of cells such that the blocking relations are fixed within each cell. We apply the approach to assembly motions of several useful types, including one-step translations, multistep translations, and infinitesimal rigid motions. Several efficiency improvements are described, as well as methods to include additional assembly constraints into the framework. The resulting algorithms have been implemented and tested extensively on complex assemblies. We conclude by describing some remaining open problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004539910025
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    Fulltext
  • 2
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    Polar and Non-Polar Layers on Mars: A Single Mechanism for Formation? (2003)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The recent discovery of vast quantities of near-subsurface ice in both polar regions of Mars by the Mars Odyssey Gamma Ray Spectrometer (GRS) has presented us with an interesting quandary. On one hand, these deposits, found poleward of 60 deg in both hemispheres, are consistent with thermal models suggesting ice will be best protected in these regions during periods of high obliquity. On the other hand, the current paradigm regarding the placement of these deposits, i.e., diffusive deposition of water vapor, appears to be inconsistent with the large volume mixing ratios (approx. 90%) inferred from the GRS data. This incongruity argues that diffusion alone cannot be the primary mechanism for the creation of these reservoirs, and that an alternate, large-scale process should be considered.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Third International Conference on Mars Polar Science and Exploration; LPI-Contrib-1184
    Format: application/pdf
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  • 3
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    The Polar Regions and Martian Climate: Studies with a Global Climate Model (2003)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Much of the interest in the polar regions centers on the fact that they likely contain the best record of Martian climate change on time scales from years to eons. This expectation is based upon the observed occurrence of weathering product deposits and volatile reservoirs that are coupled to the climate. Interpretation and understanding of these records requires understanding of the mechanisms that involve the exchange of dust, water, and carbon dioxide between the surface and atmosphere, and the atmospheric redistribution of these species. We will summarize our use of the GFDL Mars general circulation model (MGCM), to exploration aspects of the interaction between the global climate and the polar regions. For example, our studies have shown that while the northern polar cap is the dominant seasonal source for water, it can act as a net annual source or sink for water, depending upon the cap temperatures and the bulk humidity of the atmosphere. This behavior regulates the annual and global average humidity of the atmosphere, as the cap acts as a sink if the atmosphere is too wet and a source if it is too dry. We will then focus our presentation on the ability of the MGCM to simulate the observed diurnal variations of surface temperature. We are particularly interested in assessing the influence of dust aerosol and water ice clouds on simulated surface temperature and the comparison with observations. Surface thermal inertia and albedo are critical boundary inputs for MGCM simulations. Thermal inertia is also of intrinsic interest as it may be related to properties of the surface such as particle size and surface character.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Third International Conference on Mars Polar Science and Exploration; LPI-Contrib-1184
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  • 4
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    Daily to interannual variability in Mars' surfare pressure (2002)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Keywords: Lunar and Planetary Science and Exploration
    Type: American Geophysical Union Annual Fall Meeting; San Francisco, CA; United States
    Format: text
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  • 5
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    Explaining the Mid-Latitude Ice Deposits with a General Circulation Model (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: We have examined the influence of a regolith on the water cycle with a focus on high obliquity periods on Mars. Our findings show that while the regolith will almost certainly interact with the atmosphere initially, it is only a transient effect, and ice will form on the surface once the regolith is effectively isolated from the atmosphere. These low latitude deposits could conceivably be ice deposits formed at high obliquity and are certainly presently out of thermal equilibrium, but remain due to the insulating effect of a dust lag.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXV: Special Session: Mars Climate Change; LPI-Contrib-1197
    Format: text
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  • 6
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    Group Sunspot Numbers: Sunspot Cycle Characteristics (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: We examine the "Group" sunspot numbers constructed by Hoyt and Schatten to determine their utility in characterizing the solar activity cycle. We compare smoothed monthly Group Sunspot Numbers to Zurich (International) Sunspot Numbers, 10.7-cm radio flux, and total sunspot area. We find that the Zurich numbers follow the 10.7-cm radio flux and total sunspot area measurements slightly better than the Group numbers. We examine several significant characteristics of the sunspot cycle using both Group numbers and Zurich numbers. We find that the "Waldmeier Effect" - the anti-correlation between cycle amplitude and the elapsed time between minimum and maximum of a cycle - is much more apparent in the Zurich numbers. The "Amplitude-Period Effect" the anti-correlation between cycle amplitude and the length of the previous cycle from minimum to minimum - is also much more apparent in the Zurich numbers. The "Amplitude-Minimum Effect" - the correlation between cycle amplitude and the activity level at the previous (onset) minimum is equally apparent in both the Zurich numbers and the Group numbers. The "Even-Odd Effect" - in which odd-numbered cycles are larger than their even-numbered precursors - is somewhat stronger in the Group numbers but with a tighter relationship in the Zurich numbers. The "Secular Trend" - the increase in cycle amplitudes since the Maunder Minimum - is much stronger in Group numbers. After removing this trend we find little evidence for multi-cycle periodicities like the 80 year Gleissberg cycle or the two- and three-cycle periodicities. We also find little evidence for a correlation between the amplitude of a cycle and its period or for a bimodal distribution of cycle periods. We conclude that the Group numbers are most useful for extending the sunspot cycle data further back in time and thereby adding more cycles and improving the statistics. However, the Zurich numbers are more useful for characterizing the on-going levels of solar activity.
    Keywords: Solar Physics
    Format: text
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  • 7
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    Evidence that a Deep Meridional Flow Sets the Sunspot Cycle Period (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Sunspots appear on the Sun in two bands on either side of the equator that drift toward lower latitudes as each sunspot cycle progresses. We examine the equatorward drift of the centroid of the sunspot area in each hemisphere from 1874 to 2002 and find that the drift rate slows as the centroid approaches the equator. We compare the drift rate at sunspot cycle maximum to the cycle-period for each hemisphere and find a highly significant anti-correlation: hemispheres with faster drift rates have shorter periods. These observations are. consistent with an equatorward meridional counterflow, deep within the Sun, as the primary driver of the equatorward migration and the period associated with the sunspot cycle. We also find that the drift rate at maximum is significantly correlated with the amplitude of the following cycle, a prediction of dynamo models that employ a deep equatorward meridional flow. Our results indicate an amplitude of about 1.2 m/s for the meridional flow velocity at the base of the solar convection zone.
    Keywords: Solar Physics
    Type: Solar Physics Division/American Astronomical Society; Jun 16, 2003 - Jun 20, 2003; Laurel, MD; United States
    Format: text
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