26,426 research outputs found
2018 Census of California Water Transit Services
The U.S. Bureau of Transportation Statistics conducts a nationwide census of ferry boat operators for the U.S. Department of Transportation and the collected information is used for statistical purposes. The Caltrans Division of Local Assistance has been asked by the Federal Highway Administration (FHWA) to gather data regarding ferry operations under the Moving Ahead for Progress in the 21st Century Act (MAP-21). MAP-21 includes a new formula program for ferry boats and ferry terminal facilities eligible under 23 USC 129(c) which authorizes federal participation in toll roads, bridges, tunnels, and ferries. FHWA has asked that Caltrans assure the ferry boat data is current for MAP-21.The Mineta Transportation Institute was initially contacted by Caltrans to conduct this census in 2012 and a report was delivered later that year. Now the census has been completed with updates through November 2018. The research team collected information from 25 water transportation operators throughout California and produced 42 accompanying maps that depict routes and terminals where the operators provide service. Tabular information for each operator catalogs their number of vessels, passenger counts, fares, seating capacity, route lengths and other data points. Note that a number of operators, despite repeated contact via phone and email, chose not to reply.This report organizes water transportation operations into three sections based on California geography: northern California, the Sacramento Delta region; and southern California. A fourth section documents four operators who did not fall within those three geographic regions.The report concludes with a listing of recreational voyage operators (e.g. cruises, fishing trips) that the authors felt did not constitute “water transportation” for the purposes of the detailed census yet may be of interest to those applying a broader definition of water transport
Selective surface functionalization and cell uptake of reproducibly synthesized biocompatible nanocapsules
Instability of spatial patterns and its ambiguous impact on species diversity
Self-arrangement of individuals into spatial patterns often accompanies and
promotes species diversity in ecological systems. Here, we investigate pattern
formation arising from cyclic dominance of three species, operating near a
bifurcation point. In its vicinity, an Eckhaus instability occurs, leading to
convectively unstable "blurred" patterns. At the bifurcation point, stochastic
effects dominate and induce counterintuitive effects on diversity: Large
patterns, emerging for medium values of individuals' mobility, lead to rapid
species extinction, while small patterns (low mobility) promote diversity, and
high mobilities render spatial structures irrelevant. We provide a quantitative
analysis of these phenomena, employing a complex Ginzburg-Landau equation.Comment: 4 pages, 3 figures and supplementary information. To appear in Phys.
Rev. Lett
Efficient Constellation-Based Map-Merging for Semantic SLAM
Data association in SLAM is fundamentally challenging, and handling ambiguity
well is crucial to achieve robust operation in real-world environments. When
ambiguous measurements arise, conservatism often mandates that the measurement
is discarded or a new landmark is initialized rather than risking an incorrect
association. To address the inevitable `duplicate' landmarks that arise, we
present an efficient map-merging framework to detect duplicate constellations
of landmarks, providing a high-confidence loop-closure mechanism well-suited
for object-level SLAM. This approach uses an incrementally-computable
approximation of landmark uncertainty that only depends on local information in
the SLAM graph, avoiding expensive recovery of the full system covariance
matrix. This enables a search based on geometric consistency (GC) (rather than
full joint compatibility (JC)) that inexpensively reduces the search space to a
handful of `best' hypotheses. Furthermore, we reformulate the commonly-used
interpretation tree to allow for more efficient integration of clique-based
pairwise compatibility, accelerating the branch-and-bound max-cardinality
search. Our method is demonstrated to match the performance of full JC methods
at significantly-reduced computational cost, facilitating robust object-based
loop-closure over large SLAM problems.Comment: Accepted to IEEE International Conference on Robotics and Automation
(ICRA) 201
Nonaffine rubber elasticity for stiff polymer networks
We present a theory for the elasticity of cross-linked stiff polymer
networks. Stiff polymers, unlike their flexible counterparts, are highly
anisotropic elastic objects. Similar to mechanical beams stiff polymers easily
deform in bending, while they are much stiffer with respect to tensile forces
(``stretching''). Unlike in previous approaches, where network elasticity is
derived from the stretching mode, our theory properly accounts for the soft
bending response. A self-consistent effective medium approach is used to
calculate the macroscopic elastic moduli starting from a microscopic
characterization of the deformation field in terms of ``floppy modes'' --
low-energy bending excitations that retain a high degree of non-affinity. The
length-scale characterizing the emergent non-affinity is given by the ``fiber
length'' , defined as the scale over which the polymers remain straight.
The calculated scaling properties for the shear modulus are in excellent
agreement with the results of recent simulations obtained in two-dimensional
model networks. Furthermore, our theory can be applied to rationalize bulk
rheological data in reconstituted actin networks.Comment: 12 pages, 10 figures, revised Section II
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