1,337,740 research outputs found
Deep inelastic scattering from light nuclei
We review recent developments in the study of deep inelastic scattering from
light nuclei, focusing in particular on deuterium, helium, and lithium.
Understanding the nuclear effects in these systems is essential for the
extraction of information on the neutron structure function.Comment: 11 pages, 5 figures; talk given by W. Melnitchouk at the Workshop on
Testing QCD through Spin Observables in Nuclear Targets, University of
Virginia, April 200
A Deep Reinforcement Learning Framework for Rebalancing Dockless Bike Sharing Systems
Bike sharing provides an environment-friendly way for traveling and is
booming all over the world. Yet, due to the high similarity of user travel
patterns, the bike imbalance problem constantly occurs, especially for dockless
bike sharing systems, causing significant impact on service quality and company
revenue. Thus, it has become a critical task for bike sharing systems to
resolve such imbalance efficiently. In this paper, we propose a novel deep
reinforcement learning framework for incentivizing users to rebalance such
systems. We model the problem as a Markov decision process and take both
spatial and temporal features into consideration. We develop a novel deep
reinforcement learning algorithm called Hierarchical Reinforcement Pricing
(HRP), which builds upon the Deep Deterministic Policy Gradient algorithm.
Different from existing methods that often ignore spatial information and rely
heavily on accurate prediction, HRP captures both spatial and temporal
dependencies using a divide-and-conquer structure with an embedded localized
module. We conduct extensive experiments to evaluate HRP, based on a dataset
from Mobike, a major Chinese dockless bike sharing company. Results show that
HRP performs close to the 24-timeslot look-ahead optimization, and outperforms
state-of-the-art methods in both service level and bike distribution. It also
transfers well when applied to unseen areas
Graph Convolutional Neural Networks for Web-Scale Recommender Systems
Recent advancements in deep neural networks for graph-structured data have
led to state-of-the-art performance on recommender system benchmarks. However,
making these methods practical and scalable to web-scale recommendation tasks
with billions of items and hundreds of millions of users remains a challenge.
Here we describe a large-scale deep recommendation engine that we developed and
deployed at Pinterest. We develop a data-efficient Graph Convolutional Network
(GCN) algorithm PinSage, which combines efficient random walks and graph
convolutions to generate embeddings of nodes (i.e., items) that incorporate
both graph structure as well as node feature information. Compared to prior GCN
approaches, we develop a novel method based on highly efficient random walks to
structure the convolutions and design a novel training strategy that relies on
harder-and-harder training examples to improve robustness and convergence of
the model. We also develop an efficient MapReduce model inference algorithm to
generate embeddings using a trained model. We deploy PinSage at Pinterest and
train it on 7.5 billion examples on a graph with 3 billion nodes representing
pins and boards, and 18 billion edges. According to offline metrics, user
studies and A/B tests, PinSage generates higher-quality recommendations than
comparable deep learning and graph-based alternatives. To our knowledge, this
is the largest application of deep graph embeddings to date and paves the way
for a new generation of web-scale recommender systems based on graph
convolutional architectures.Comment: KDD 201
A Deep Chandra Observation of the Distant Galaxy Cluster MS1137.5+6625
We present results from a deep Chandra observation of MS1137.5+66, a distant
(z=0.783) and massive cluster of galaxies. Only a few similarly massive
clusters are currently known at such high redshifts; accordingly, this
observation provides much-needed information on the dynamical state of these
rare systems. The cluster appears both regular and symmetric in the X-ray
image. However, our analysis of the spectral and spatial X-ray data in
conjunction with interferometric Sunyaev-Zel'dovich effect data and published
deep optical imaging suggests the cluster has a fairly complex structure. The
angular diameter distance we calculate from the Chandra and Sunyaev-Zel'dovich
effect data assuming an isothermal, spherically symmetric cluster implies a low
value for the Hubble constant for which we explore possible explanations.Comment: 16 pages, 6 figures, submitted to Ap
The Time Structure of Hadronic Showers in Imaging Calorimeters with Scintillator and RPC Readout
The intrinsic time structure of hadronic showers has been studied to evaluate
its influence on the timing capability and on the required integration time of
highly granular hadronic calorimeters in future collider experiments. The
experiments have been carried with systems of 15 detector cells, using both
scintillator tiles with SiPM readout and RPCs, read out with fast digitizers
and deep buffers. These were installed behind the CALICE scintillator -
Tungsten and RPC - Tungsten calorimeters as well as behind the CALICE
semi-digital RPC - Steel calorimeter during test beam periods at the CERN SPS.
We will discuss the technical aspects of these systems, and present results on
the measurement of the time structure of hadronic showers in steel and tungsten
calorimeters. These are compared to GEANT4 simulations, providing important
information for the validation and the improvement of the physics models. In
addition, a comparison of the observed time structure with scintillator and RPC
active elements will be presented, which provides insight into the differences
in sensitivity to certain aspects of hadronic showers depending on readout
technology.Comment: 8 pages, 6 figures, proceedings for CHEF2013, Paris, France, April
201
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