13,266 research outputs found
Communication-Optimal Distributed Dynamic Graph Clustering
We consider the problem of clustering graph nodes over large-scale dynamic
graphs, such as citation networks, images and web networks, when graph updates
such as node/edge insertions/deletions are observed distributively. We propose
communication-efficient algorithms for two well-established communication
models namely the message passing and the blackboard models. Given a graph with
nodes that is observed at remote sites over time , the two
proposed algorithms have communication costs and
( hides a polylogarithmic factor), almost matching
their lower bounds, and , respectively, in the
message passing and the blackboard models. More importantly, we prove that at
each time point in our algorithms generate clustering quality nearly as
good as that of centralizing all updates up to that time and then applying a
standard centralized clustering algorithm. We conducted extensive experiments
on both synthetic and real-life datasets which confirmed the communication
efficiency of our approach over baseline algorithms while achieving comparable
clustering results.Comment: Accepted and to appear in AAAI'1
The Photophysical Properties of Squaraine Derivatives and Their Impact upon Photovoltaic Efficiencies
Squaraine dyes provide potential on improving the efficiency of Organic photovoltaic OPV solar cell. Characterization of the photophysical properties of squaraine dyes is going to help us find the best material for our device. A series of squaraines (DESQ(OH)2, DiBSQ(OH)2, and novel DiPSQ(OH)2) in which side chains length increasing were characterized in this paper. The material photophysical properties of these squaraines were systematically characterized using various tools. Our research showed that the length of side chain plays an important role in aggregation properties of squaraines, longer side chains result in smaller exciton splitting and hence less broadened absorbance spectrum. Interestingly, DiPSQ(OH)2 which has the longest side chains unexpectedly gave the most broadened absorbance spectrum in aggregation. The impact of aggregation on fluorescence was also studied, we demonstrated that the squaraines lost fluorescence before a pure solid state was reached. We attribute this to the formation of some kind long range aggregate
Improved transient simulation of salient-pole synchronous generators with internal and ground faults in the stator winding
An improved model for simulating the transient behavior of salient-pole synchronous generators with internal and ground faults in the stator winding is established using the multi-loop circuit method. The model caters for faults under different ground conditions for the neutral, and accounts for the distributed capacitances of the windings to ground. Predictions from the model are validated by experiments, and it is shown that the model accurately predicts the voltage and current waveforms under fault conditions. Hence, it can be used to analyze important features of faults and to design appropriate protection schemes
Response of 20 laterally loaded piles in sand
Closed-form solutions and their associated spreadsheet program (GASLFP) were developed by the first author for laterally loaded free- head piles in elastic-plastic media. The solutions show behaviour of a laterally loaded pile is dominated by net limiting force per unit length (LFP) fully mobilised along the pile to a depth called slip depth. They are characterised by three parameters of Ng, α o and n (to describe the LFP) and the soil shear modulus (Gs). Conversely, these parameters may be deduced by matching the predicted with measured response. To facilitate practical design, in this paper, the input values of Ng, α o, n and Gs were deduced in light of measured response of 20 piles tested in sand. The result allows effect of pile types, installation action, and dry or submerged sand to be clarified. In addition, using analogy to pipeline-soil interaction, a new alternative expression described by the parameters kp, α o and n is proposed to construct the LFP. The use of the previous parameter Ng and the new kp is discussed at length. Critical responses for typical deflection levels have also been provided. This back-analysis is elaborated via three typical cases
An Efficient Algorithm for Deep Stochastic Contextual Bandits
In stochastic contextual bandit (SCB) problems, an agent selects an action
based on certain observed context to maximize the cumulative reward over
iterations. Recently there have been a few studies using a deep neural network
(DNN) to predict the expected reward for an action, and the DNN is trained by a
stochastic gradient based method. However, convergence analysis has been
greatly ignored to examine whether and where these methods converge. In this
work, we formulate the SCB that uses a DNN reward function as a non-convex
stochastic optimization problem, and design a stage-wise stochastic gradient
descent algorithm to optimize the problem and determine the action policy. We
prove that with high probability, the action sequence chosen by this algorithm
converges to a greedy action policy respecting a local optimal reward function.
Extensive experiments have been performed to demonstrate the effectiveness and
efficiency of the proposed algorithm on multiple real-world datasets.Comment: Accepted by AAAI 202
Gamma rays and neutrinos from dark matter annihilation in galaxy clusters
The -ray and neutrino emissions from dark matter (DM) annihilation in
galaxy clusters are studied. After about one year operation of Fermi-LAT,
several nearby clusters are reported with stringent upper limits of GeV
-ray emission. We use the Fermi-LAT upper limits of these clusters to
constrain the DM model parameters. We find that the DM model distributed with
substructures predicted in cold DM (CDM) scenario is strongly constrained by
Fermi-LAT -ray data. Especially for the leptonic annihilation scenario
which may account for the excesses discovered by
PAMELA/Fermi-LAT/HESS, the constraint on the minimum mass of substructures is
of the level M, which is much larger than that expected
in CDM picture, but is consistent with a warm DM scenario. We further
investigate the sensitivity of neutrino detections of the clusters by IceCube.
It is found that neutrino detection is much more difficult than -rays.
Only for very heavy DM ( TeV) together with a considerable branching
ratio to line neutrinos the neutrino sensitivity is comparable with that of
-rays.Comment: 21 pages, 8 figures and 1 table; extended discussion about the
uncertainties of concentration and subhalo models, figures replotted for
better read; references updated; accepted for publication by Phys. Rev.
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