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Automatic Generation of School Bus Routes in Los Angeles
The goal of our project is to automatically generate school bus routes for the Los Angeles Unified School District (LAUSD). We examined four algorithms, including two from the existing literature and two new ones that we developed. A major focus of our work was the construction of “mixed-load routes,” which transport students from multiple schools. Based on our measurements (whose imperfections we discuss), three of the four algorithms perform at least as well as the existing route plan, and one of those three performs better than the existing route plan. We also delivered a user-friendly routing program to LAUSD that uses one of these algorithms, and we have made our software publicly available. Our insights and results are also applicable to other school districts that permit mixed-load routing
Space Station alpha joint bearing
Perhaps the most critical structural system aboard the Space Station is the Solar Alpha Rotary Joint which helps align the power generation system with the sun. The joint must provide structural support and controlled rotation to the outboard transverse booms as well as power and data transfer across the joint. The Solar Alpha Rotary Joint is composed of two transition sections and an integral, large diameter bearing. Alpha joint bearing design presents a particularly interesting problem because of its large size and need for high reliability, stiffness, and on orbit maintability. The discrete roller bearing developed is a novel refinement to cam follower technology. It offers thermal compensation and ease of on-orbit maintenance that are not found in conventional rolling element bearings. How the bearing design evolved is summarized. Driving requirements are reviewed, alternative concepts assessed, and the selected design is described
Helical magnetic structure and the anomalous and topological Hall effects in epitaxial B20 FeCoGe films
Epitaxial films of the B20-structure alloy FeCoGe were grown by
molecular beam epitaxy on Si (111) substrates. The magnetization varied
smoothly from the bulk-like values of one Bohr magneton per Fe atom for FeGe to
zero for non-magnetic CoGe. The chiral lattice structure leads to a
Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground
state was confirmed using polarized neutron reflectometry measurements. The
pitch of the spin helix, measured by this method, varies with Co content
and diverges at . This indicates a zero-crossing of the DMI, which
we reproduced in calculations using first principle methods. We also measured
the longitudinal and Hall resistivity of our films as a function of magnetic
field, temperature, and Co content . The Hall resistivity is expected to
contain contributions from the ordinary, anomalous, and topological Hall
effects. Both the anomalous and topological Hall resistivities show peaks
around . Our first principles calculations show a peak in the
topological Hall constant at this value of , related to the strong
spin-polarisation predicted for intermediate values of . Half-metallicity is
predicted for , consistent with the experimentally observed linear
magnetoresistance at this composition. Whilst it is possible to reconcile
theory with experiment for the various Hall effects for FeGe, the large
topological Hall resistivities for are much larger then expected
when the very small emergent fields associated with the divergence in the DMI
are taken into account
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