1,810 research outputs found
Analysis of AVHRR, CZCS and historical in situ data off the Oregon Coast
The original scientific objectives of this grant were to: (1) characterize the seasonal cycles and interannual variability for phytoplankton concentrations and sea surface temperature (SST) in the California Current using satellite data; and (2) to explore the spatial and temporal relationship between these variables and surface wind forcing. An additional methodological objective was to develop statistical methods for forming mean fields, which minimize the effects of random data gaps and errors in the irregularly sampled CZCS (Coastal Zone Color Scanner) and AVHRR (Advanced Very High Resolution Radiometer) satellite data. A final task was to evaluate the level of uncertainty in the wind fields used for the statistical analysis. Funding in the first year included part of the cost of an image processing system to enable this and other projects to process and analyze satellite data. This report consists of summaries of the major projects carried out with all or partial support from this grant. The appendices include a list of papers and professional presentations supported by the grant, as well as reprints of the major papers and reports
Advanced BIT* (ABIT*): Sampling-Based Planning with Advanced Graph-Search Techniques
Path planning is an active area of research essential for many applications
in robotics. Popular techniques include graph-based searches and sampling-based
planners. These approaches are powerful but have limitations. This paper
continues work to combine their strengths and mitigate their limitations using
a unified planning paradigm. It does this by viewing the path planning problem
as the two subproblems of search and approximation and using advanced
graph-search techniques on a sampling-based approximation. This perspective
leads to Advanced BIT*. ABIT* combines truncated anytime graph-based searches,
such as ATD*, with anytime almost-surely asymptotically optimal sampling-based
planners, such as RRT*. This allows it to quickly find initial solutions and
then converge towards the optimum in an anytime manner. ABIT* outperforms
existing single-query, sampling-based planners on the tested problems in
and , and was demonstrated on real-world
problems with NASA/JPL-Caltech.Comment: IEEE International Conference on Robotics and Automation (ICRA) 2020,
6 + 1 pages, 3 figures, video available at https://youtu.be/VFdihv8Lq2
Adaptively Informed Trees (AIT*): Fast Asymptotically Optimal Path Planning through Adaptive Heuristics
Informed sampling-based planning algorithms exploit problem knowledge for
better search performance. This knowledge is often expressed as heuristic
estimates of solution cost and used to order the search. The practical
improvement of this informed search depends on the accuracy of the heuristic.
Selecting an appropriate heuristic is difficult. Heuristics applicable to an
entire problem domain are often simple to define and inexpensive to evaluate
but may not be beneficial for a specific problem instance. Heuristics specific
to a problem instance are often difficult to define or expensive to evaluate
but can make the search itself trivial.
This paper presents Adaptively Informed Trees (AIT*), an almost-surely
asymptotically optimal sampling-based planner based on BIT*. AIT* adapts its
search to each problem instance by using an asymmetric bidirectional search to
simultaneously estimate and exploit a problem-specific heuristic. This allows
it to quickly find initial solutions and converge towards the optimum. AIT*
solves the tested problems as fast as RRT-Connect while also converging towards
the optimum.Comment: IEEE International Conference on Robotics and Automation (ICRA) 2020,
6 + 2 pages, 5 figures, video available at https://youtu.be/twM723QM9T
Asymptotically Optimal Sampling-Based Motion Planning Methods
Motion planning is a fundamental problem in autonomous robotics that requires
finding a path to a specified goal that avoids obstacles and takes into account
a robot's limitations and constraints. It is often desirable for this path to
also optimize a cost function, such as path length.
Formal path-quality guarantees for continuously valued search spaces are an
active area of research interest. Recent results have proven that some
sampling-based planning methods probabilistically converge toward the optimal
solution as computational effort approaches infinity. This survey summarizes
the assumptions behind these popular asymptotically optimal techniques and
provides an introduction to the significant ongoing research on this topic.Comment: Posted with permission from the Annual Review of Control, Robotics,
and Autonomous Systems, Volume 4. Copyright 2021 by Annual Reviews,
https://www.annualreviews.org/. 25 pages. 2 figure
Gene induction during differentiation of human monocytes into dendritic cells: an integrated study at the RNA and protein levels
Changes in gene expression occurring during differentiation of human
monocytes into dendritic cells were studied at the RNA and protein levels.
These studies showed the induction of several gene classes corresponding to
various biological functions. These functions encompass antigen processing and
presentation, cytoskeleton, cell signalling and signal transduction, but also
an increase in mitochondrial function and in the protein synthesis machinery,
including some, but not all, chaperones. These changes put in perspective the
events occurring during this differentiation process. On a more technical
point, it appears that the studies carried out at the RNA and protein levels
are highly complementary.Comment: website publisher:
http://www.springerlink.com/content/ha0d2c351qhjhjdm
Seasonal Climatology of Hydrographic Conditions in the Upwelling Region Off Northern Chile
Over 30 years of hydrographic data from the northern Chile (18 degreesS-24 degreesS) upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore. The data are interpolated to a grid with sufficient spatial resolution to preserve cross-shelf gradients and then presented as means within four seasons: austral winter (July-September), spring (October-December), summer (January-March), and fall (April-June). Climatological monthly wind forcing, surface temperature, and sea level from three coastal stations indicate equatorward (upwelling favorable) winds throughout the year, weakest in the north. Seasonal maximum alongshore wind stress is in late spring and summer (December-March). Major water masses of the region are identified in climatological T-S plots and their sources and implied circulation discussed. Surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year-round, strongest in summer and weakest in winter, bringing relatively fresh water to the surface nearshore. Surface geostrophic flow nearshore is equatorward throughout the year. During summer, an anticyclonic circulation feature in the north which extends to at least 200 m depth is evident in geopotential anomaly and in both temperature and geopotential variance fields. Subsurface fields indicate generally poleward flow throughout the year, strongest in an undercurrent near the coast. This undercurrent is strongest in summer and most persistent and organized in the south (south of 21 degreesS), A subsurface oxygen minimum, centered at similar to 250 m, is strongest at lower latitudes. Low-salinity subsurface water intrudes into the study area near 100 m, predominantly in offshore regions, strongest during summer and fall and in the southernmost portion of the region. The climatological fields are compared to features off Baja within the somewhat analogous California Current and to measurements from higher latitudes within the Chile-Peru Current system
Seasonal Climatology of Hydrographic Conditions in the Upwelling Region Off Northern Chile
Over 30 years of hydrographic data from the northern Chile (18°S-24°S) upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore. The data are interpolated to a grid with sufficient spatial resolution to preserve crossshelf gradients and then presented as means within four seasons: austral winter (JulySeptember), spring (October-December), summer (January-March), and fall (April-June). Climatological monthly wind forcing, surface temperature, and sea level from three coastal stations indicate equatorward (upwelling favorable) winds throughout the year, weakest in the north. Seasonal maximum alongshore wind stress is in late spring and summer (DecemberMarch). Major water masses of the region are identified in climatological T-S plots and their sources and implied circulation discussed. Surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year-round, strongest in summer and weakest in winter, bringing relatively fresh water to the surface nearshore. Surface geostrophic flow nearshore is equatorward throughout the year. During summer, an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields. Subsurface fields indicate generally poleward flow throughout the year, strongest in an undercurrent near the coast. This undercurrent is strongest in summer and most persistent and organized in the south (south of 21°S). A subsurface oxygen minimum, centered at ~250 m, is strongest at lower latitudes. Low-salinity subsurface water intrudes into the study area near 100 m, predominantly in offshore regions, strongest during summer and fall and in the southernmost portion of the region. The climatological fields are compared to features off Baja within the somewhat analogous California Current and to measurements from higher latitudes within the Chile-Peru Current system. Copyright 2001 by the American Geophysiccal Union
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