37,516 research outputs found
Latent Space Model for Multi-Modal Social Data
With the emergence of social networking services, researchers enjoy the
increasing availability of large-scale heterogenous datasets capturing online
user interactions and behaviors. Traditional analysis of techno-social systems
data has focused mainly on describing either the dynamics of social
interactions, or the attributes and behaviors of the users. However,
overwhelming empirical evidence suggests that the two dimensions affect one
another, and therefore they should be jointly modeled and analyzed in a
multi-modal framework. The benefits of such an approach include the ability to
build better predictive models, leveraging social network information as well
as user behavioral signals. To this purpose, here we propose the Constrained
Latent Space Model (CLSM), a generalized framework that combines Mixed
Membership Stochastic Blockmodels (MMSB) and Latent Dirichlet Allocation (LDA)
incorporating a constraint that forces the latent space to concurrently
describe the multiple data modalities. We derive an efficient inference
algorithm based on Variational Expectation Maximization that has a
computational cost linear in the size of the network, thus making it feasible
to analyze massive social datasets. We validate the proposed framework on two
problems: prediction of social interactions from user attributes and behaviors,
and behavior prediction exploiting network information. We perform experiments
with a variety of multi-modal social systems, spanning location-based social
networks (Gowalla), social media services (Instagram, Orkut), e-commerce and
review sites (Amazon, Ciao), and finally citation networks (Cora). The results
indicate significant improvement in prediction accuracy over state of the art
methods, and demonstrate the flexibility of the proposed approach for
addressing a variety of different learning problems commonly occurring with
multi-modal social data.Comment: 12 pages, 7 figures, 2 table
Optical tomography: Image improvement using mixed projection of parallel and fan beam modes
Mixed parallel and fan beam projection is a technique used to increase the quality images. This research focuses on enhancing the image quality in optical tomography. Image quality can be deļ¬ned by measuring the Peak Signal to Noise Ratio (PSNR) and Normalized Mean Square Error (NMSE) parameters. The ļ¬ndings of this research prove that by combining parallel and fan beam projection, the image quality can be increased by more than 10%in terms of its PSNR value and more than 100% in terms of its NMSE value compared to a single parallel beam
Multi-rendezvous Spacecraft Trajectory Optimization with Beam P-ACO
The design of spacecraft trajectories for missions visiting multiple
celestial bodies is here framed as a multi-objective bilevel optimization
problem. A comparative study is performed to assess the performance of
different Beam Search algorithms at tackling the combinatorial problem of
finding the ideal sequence of bodies. Special focus is placed on the
development of a new hybridization between Beam Search and the Population-based
Ant Colony Optimization algorithm. An experimental evaluation shows all
algorithms achieving exceptional performance on a hard benchmark problem. It is
found that a properly tuned deterministic Beam Search always outperforms the
remaining variants. Beam P-ACO, however, demonstrates lower parameter
sensitivity, while offering superior worst-case performance. Being an anytime
algorithm, it is then found to be the preferable choice for certain practical
applications.Comment: Code available at https://github.com/lfsimoes/beam_paco__gtoc
Scientific impact evaluation and the effect of self-citations: mitigating the bias by discounting h-index
In this paper, we propose a measure to assess scientific impact that
discounts self-citations and does not require any prior knowledge on the their
distribution among publications. This index can be applied to both researchers
and journals. In particular, we show that it fills the gap of h-index and
similar measures that do not take into account the effect of self-citations for
authors or journals impact evaluation. The paper provides with two real-world
examples: in the former, we evaluate the research impact of the most productive
scholars in Computer Science (according to DBLP); in the latter, we revisit the
impact of the journals ranked in the 'Computer Science Applications' section of
SCImago. We observe how self-citations, in many cases, affect the rankings
obtained according to different measures (including h-index and ch-index), and
show how the proposed measure mitigates this effect
Uncovering nodes that spread information between communities in social networks
From many datasets gathered in online social networks, well defined community
structures have been observed. A large number of users participate in these
networks and the size of the resulting graphs poses computational challenges.
There is a particular demand in identifying the nodes responsible for
information flow between communities; for example, in temporal Twitter networks
edges between communities play a key role in propagating spikes of activity
when the connectivity between communities is sparse and few edges exist between
different clusters of nodes. The new algorithm proposed here is aimed at
revealing these key connections by measuring a node's vicinity to nodes of
another community. We look at the nodes which have edges in more than one
community and the locality of nodes around them which influence the information
received and broadcasted to them. The method relies on independent random walks
of a chosen fixed number of steps, originating from nodes with edges in more
than one community. For the large networks that we have in mind, existing
measures such as betweenness centrality are difficult to compute, even with
recent methods that approximate the large number of operations required. We
therefore design an algorithm that scales up to the demand of current big data
requirements and has the ability to harness parallel processing capabilities.
The new algorithm is illustrated on synthetic data, where results can be judged
carefully, and also on a real, large scale Twitter activity data, where new
insights can be gained
Analysis of Computer Science Communities Based on DBLP
It is popular nowadays to bring techniques from bibliometrics and
scientometrics into the world of digital libraries to analyze the collaboration
patterns and explore mechanisms which underlie community development. In this
paper we use the DBLP data to investigate the author's scientific career and
provide an in-depth exploration of some of the computer science communities. We
compare them in terms of productivity, population stability and collaboration
trends.Besides we use these features to compare the sets of topranked
conferences with their lower ranked counterparts.Comment: 9 pages, 7 figures, 6 table
- ā¦