165,147 research outputs found
STWalk: Learning Trajectory Representations in Temporal Graphs
Analyzing the temporal behavior of nodes in time-varying graphs is useful for
many applications such as targeted advertising, community evolution and outlier
detection. In this paper, we present a novel approach, STWalk, for learning
trajectory representations of nodes in temporal graphs. The proposed framework
makes use of structural properties of graphs at current and previous time-steps
to learn effective node trajectory representations. STWalk performs random
walks on a graph at a given time step (called space-walk) as well as on graphs
from past time-steps (called time-walk) to capture the spatio-temporal behavior
of nodes. We propose two variants of STWalk to learn trajectory
representations. In one algorithm, we perform space-walk and time-walk as part
of a single step. In the other variant, we perform space-walk and time-walk
separately and combine the learned representations to get the final trajectory
embedding. Extensive experiments on three real-world temporal graph datasets
validate the effectiveness of the learned representations when compared to
three baseline methods. We also show the goodness of the learned trajectory
embeddings for change point detection, as well as demonstrate that arithmetic
operations on these trajectory representations yield interesting and
interpretable results.Comment: 10 pages, 5 figures, 2 table
Counting Causal Paths in Big Times Series Data on Networks
Graph or network representations are an important foundation for data mining
and machine learning tasks in relational data. Many tools of network analysis,
like centrality measures, information ranking, or cluster detection rest on the
assumption that links capture direct influence, and that paths represent
possible indirect influence. This assumption is invalidated in time-stamped
network data capturing, e.g., dynamic social networks, biological sequences or
financial transactions. In such data, for two time-stamped links (A,B) and
(B,C) the chronological ordering and timing determines whether a causal path
from node A via B to C exists. A number of works has shown that for that reason
network analysis cannot be directly applied to time-stamped network data.
Existing methods to address this issue require statistics on causal paths,
which is computationally challenging for big data sets.
Addressing this problem, we develop an efficient algorithm to count causal
paths in time-stamped network data. Applying it to empirical data, we show that
our method is more efficient than a baseline method implemented in an
OpenSource data analytics package. Our method works efficiently for different
values of the maximum time difference between consecutive links of a causal
path and supports streaming scenarios. With it, we are closing a gap that
hinders an efficient analysis of big time series data on complex networks.Comment: 10 pages, 2 figure
A Lightweight Distributed Solution to Content Replication in Mobile Networks
Performance and reliability of content access in mobile networks is
conditioned by the number and location of content replicas deployed at the
network nodes. Facility location theory has been the traditional, centralized
approach to study content replication: computing the number and placement of
replicas in a network can be cast as an uncapacitated facility location
problem. The endeavour of this work is to design a distributed, lightweight
solution to the above joint optimization problem, while taking into account the
network dynamics. In particular, we devise a mechanism that lets nodes share
the burden of storing and providing content, so as to achieve load balancing,
and decide whether to replicate or drop the information so as to adapt to a
dynamic content demand and time-varying topology. We evaluate our mechanism
through simulation, by exploring a wide range of settings and studying
realistic content access mechanisms that go beyond the traditional
assumptionmatching demand points to their closest content replica. Results show
that our mechanism, which uses local measurements only, is: (i) extremely
precise in approximating an optimal solution to content placement and
replication; (ii) robust against network mobility; (iii) flexible in
accommodating various content access patterns, including variation in time and
space of the content demand.Comment: 12 page
Bio-Inspired Multi-Layer Spiking Neural Network Extracts Discriminative Features from Speech Signals
Spiking neural networks (SNNs) enable power-efficient implementations due to
their sparse, spike-based coding scheme. This paper develops a bio-inspired SNN
that uses unsupervised learning to extract discriminative features from speech
signals, which can subsequently be used in a classifier. The architecture
consists of a spiking convolutional/pooling layer followed by a fully connected
spiking layer for feature discovery. The convolutional layer of leaky,
integrate-and-fire (LIF) neurons represents primary acoustic features. The
fully connected layer is equipped with a probabilistic spike-timing-dependent
plasticity learning rule. This layer represents the discriminative features
through probabilistic, LIF neurons. To assess the discriminative power of the
learned features, they are used in a hidden Markov model (HMM) for spoken digit
recognition. The experimental results show performance above 96% that compares
favorably with popular statistical feature extraction methods. Our results
provide a novel demonstration of unsupervised feature acquisition in an SNN
Large-Scale User Modeling with Recurrent Neural Networks for Music Discovery on Multiple Time Scales
The amount of content on online music streaming platforms is immense, and
most users only access a tiny fraction of this content. Recommender systems are
the application of choice to open up the collection to these users.
Collaborative filtering has the disadvantage that it relies on explicit
ratings, which are often unavailable, and generally disregards the temporal
nature of music consumption. On the other hand, item co-occurrence algorithms,
such as the recently introduced word2vec-based recommenders, are typically left
without an effective user representation. In this paper, we present a new
approach to model users through recurrent neural networks by sequentially
processing consumed items, represented by any type of embeddings and other
context features. This way we obtain semantically rich user representations,
which capture a user's musical taste over time. Our experimental analysis on
large-scale user data shows that our model can be used to predict future songs
a user will likely listen to, both in the short and long term.Comment: Author pre-print version, 20 pages, 6 figures, 4 table
Presurgical thalamic hubness predicts surgical outcome in temporal lobe epilepsy.
OBJECTIVE: To characterize the presurgical brain functional architecture presented in patients with temporal lobe epilepsy (TLE) using graph theoretical measures of resting-state fMRI data and to test its association with surgical outcome.
METHODS: Fifty-six unilateral patients with TLE, who subsequently underwent anterior temporal lobectomy and were classified as obtaining a seizure-free (Engel class I, n = 35) vs not seizure-free (Engel classes II-IV, n = 21) outcome at 1 year after surgery, and 28 matched healthy controls were enrolled. On the basis of their presurgical resting-state functional connectivity, network properties, including nodal hubness (importance of a node to the network; degree, betweenness, and eigenvector centralities) and integration (global efficiency), were estimated and compared across our experimental groups. Cross-validations with support vector machine (SVM) were used to examine whether selective nodal hubness exceeded standard clinical characteristics in outcome prediction.
RESULTS: Compared to the seizure-free patients and healthy controls, the not seizure-free patients displayed a specific increase in nodal hubness (degree and eigenvector centralities) involving both the ipsilateral and contralateral thalami, contributed by an increase in the number of connections to regions distributed mostly in the contralateral hemisphere. Simulating removal of thalamus reduced network integration more dramatically in not seizure-free patients. Lastly, SVM models built on these thalamic hubness measures produced 76% prediction accuracy, while models built with standard clinical variables yielded only 58% accuracy (both were cross-validated).
CONCLUSIONS: A thalamic network associated with seizure recurrence may already be established presurgically. Thalamic hubness can serve as a potential biomarker of surgical outcome, outperforming the clinical characteristics commonly used in epilepsy surgery centers
DeepCity: A Feature Learning Framework for Mining Location Check-ins
Online social networks being extended to geographical space has resulted in
large amount of user check-in data. Understanding check-ins can help to build
appealing applications, such as location recommendation. In this paper, we
propose DeepCity, a feature learning framework based on deep learning, to
profile users and locations, with respect to user demographic and location
category prediction. Both of the predictions are essential for social network
companies to increase user engagement. The key contribution of DeepCity is the
proposal of task-specific random walk which uses the location and user
properties to guide the feature learning to be specific to each prediction
task. Experiments conducted on 42M check-ins in three cities collected from
Instagram have shown that DeepCity achieves a superior performance and
outperforms other baseline models significantly
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