2,147 research outputs found
A Decomposition Algorithm to Solve the Multi-Hop Peer-to-Peer Ride-Matching Problem
In this paper, we mathematically model the multi-hop Peer-to-Peer (P2P)
ride-matching problem as a binary program. We formulate this problem as a
many-to-many problem in which a rider can travel by transferring between
multiple drivers, and a driver can carry multiple riders. We propose a
pre-processing procedure to reduce the size of the problem, and devise a
decomposition algorithm to solve the original ride-matching problem to
optimality by means of solving multiple smaller problems. We conduct extensive
numerical experiments to demonstrate the computational efficiency of the
proposed algorithm and show its practical applicability to reasonably-sized
dynamic ride-matching contexts. Finally, in the interest of even lower solution
times, we propose heuristic solution methods, and investigate the trade-offs
between solution time and accuracy
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Computer Generation of Metal Components by Simultaneous Deposition of Mould, Cores and Part
A new solid freeforming method based on co-delivery of mould powder materials and part
powder materials using vibration-controlled, dry powder valves is presented in this paper. Thin
layers of stainless steel powder are delivered to the forming area according to the cross-section of
the CAD file to produce the component. Mould powder which has low sinterability is delivered to
the non-forming areas of the same layer. All powders are delivered by computer-controlled,
acoustic powder valves. The flow rate and switching of the valves provides the composition and
shape control during fabrication. The stacked layers of loose powder are then sintered in a
conventional furnace. The mould materials are removed after sintering. This method avoids the
high thermal stress problem in selective laser sintering, avoids high capitalisation, makes use of
conventional furnaces and allows for the incorporation of three dimensional function gradients.
Test pieces including step wedge and Spierpinski’s cube were fabricated. Advantages, limitations
and problems are discussed.Mechanical Engineerin
Extremal Charged Rotating Black Holes in Odd Dimensions
Employing higher order perturbation theory, we obtain charged rotating black
holes in odd dimensions, where the Einstein-Maxwell Lagrangian may be
supplemented with a Chern-Simons term. Starting from the Myers-Perry solutions,
we use the electric charge as the perturbative parameter, and focus on extremal
black holes with equal-magnitude angular momenta. For
Einstein-Maxwell-Chern-Simons theory with arbitrary Chern-Simons coupling
constant, we perform the perturbations up to third order for any odd dimension.
We discuss the physical properties of these black holes and study their
dependence on the charge. In particular, we show that the gyromagnetic ratio
of Einstein-Maxwell black holes differs from the lowest order perturbative
value , and that the first correction term to is universal.Comment: 24 pages, 3 figure
Log-Euclidean Bag of Words for Human Action Recognition
Representing videos by densely extracted local space-time features has
recently become a popular approach for analysing actions. In this paper, we
tackle the problem of categorising human actions by devising Bag of Words (BoW)
models based on covariance matrices of spatio-temporal features, with the
features formed from histograms of optical flow. Since covariance matrices form
a special type of Riemannian manifold, the space of Symmetric Positive Definite
(SPD) matrices, non-Euclidean geometry should be taken into account while
discriminating between covariance matrices. To this end, we propose to embed
SPD manifolds to Euclidean spaces via a diffeomorphism and extend the BoW
approach to its Riemannian version. The proposed BoW approach takes into
account the manifold geometry of SPD matrices during the generation of the
codebook and histograms. Experiments on challenging human action datasets show
that the proposed method obtains notable improvements in discrimination
accuracy, in comparison to several state-of-the-art methods
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