1,745 research outputs found
k-server via multiscale entropic regularization
We present an -competitive randomized algorithm for the
-server problem on hierarchically separated trees (HSTs). This is the first
-competitive randomized algorithm for which the competitive ratio is
independent of the size of the underlying HST. Our algorithm is designed in the
framework of online mirror descent where the mirror map is a multiscale
entropy. When combined with Bartal's static HST embedding reduction, this leads
to an -competitive algorithm on any -point metric
space. We give a new dynamic HST embedding that yields an -competitive algorithm on any metric space where the ratio of the
largest to smallest non-zero distance is at most
High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures
We report experimental measurements for ultrathin (< 15 nm) van der Waals
heterostructures exhibiting external quantum efficiencies exceeding 50%, and
show that these structures can achieve experimental absorbance > 90%. By
coupling electromagnetic simulations and experimental measurements, we show
that pn WSe2/MoS2 heterojunctions with vertical carrier collection can have
internal photocarrier collection efficiencies exceeding 70%.Comment: ACS Nano, 2017. Manuscript (25 pages, 7 figures) plus supporting
information (7 pages, 4 figures
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