109 research outputs found
Global soil moisture bimodality in satellite observations and climate models
A new diagnostic metric based on soil moisture bimodality is developed in order to examine and compare soil moisture from satellite observations and Earth System Models. The methodology to derive this diagnostic is based on maximum likelihood estimator encoded into an iterative algorithm, which is applied to the soil moisture probability density function. This metric is applied to satellite data from the Advanced Microwave Scanning Radiometer for the Earth Observing System and global climate models data from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Results show high soil moisture bimodality in transitional climate areas and high latitudes, potentially associated with land-atmosphere feedback processes. When comparing satellite versus climate models, a clear difference in their soil moisture bimodality is observed, with systematically higher values in the case of CMIP5 models. These differences appear related to areas where land-atmospheric feedback may be overestimated in current climate models
Hate is not Binary: Studying Abusive Behavior of #GamerGate on Twitter
Over the past few years, online bullying and aggression have become
increasingly prominent, and manifested in many different forms on social media.
However, there is little work analyzing the characteristics of abusive users
and what distinguishes them from typical social media users. In this paper, we
start addressing this gap by analyzing tweets containing a great large amount
of abusiveness. We focus on a Twitter dataset revolving around the Gamergate
controversy, which led to many incidents of cyberbullying and cyberaggression
on various gaming and social media platforms. We study the properties of the
users tweeting about Gamergate, the content they post, and the differences in
their behavior compared to typical Twitter users.
We find that while their tweets are often seemingly about aggressive and
hateful subjects, "Gamergaters" do not exhibit common expressions of online
anger, and in fact primarily differ from typical users in that their tweets are
less joyful. They are also more engaged than typical Twitter users, which is an
indication as to how and why this controversy is still ongoing. Surprisingly,
we find that Gamergaters are less likely to be suspended by Twitter, thus we
analyze their properties to identify differences from typical users and what
may have led to their suspension. We perform an unsupervised machine learning
analysis to detect clusters of users who, though currently active, could be
considered for suspension since they exhibit similar behaviors with suspended
users. Finally, we confirm the usefulness of our analyzed features by emulating
the Twitter suspension mechanism with a supervised learning method, achieving
very good precision and recall.Comment: In 28th ACM Conference on Hypertext and Social Media (ACM HyperText
2017
Distributed estimation from relative measurements of heterogeneous and uncertain quality
This paper studies the problem of estimation from relative measurements in a
graph, in which a vector indexed over the nodes has to be reconstructed from
pairwise measurements of differences between its components associated to nodes
connected by an edge. In order to model heterogeneity and uncertainty of the
measurements, we assume them to be affected by additive noise distributed
according to a Gaussian mixture. In this original setup, we formulate the
problem of computing the Maximum-Likelihood (ML) estimates and we design two
novel algorithms, based on Least Squares regression and
Expectation-Maximization (EM). The first algorithm (LS- EM) is centralized and
performs the estimation from relative measurements, the soft classification of
the measurements, and the estimation of the noise parameters. The second
algorithm (Distributed LS-EM) is distributed and performs estimation and soft
classification of the measurements, but requires the knowledge of the noise
parameters. We provide rigorous proofs of convergence of both algorithms and we
present numerical experiments to evaluate and compare their performance with
classical solutions. The experiments show the robustness of the proposed
methods against different kinds of noise and, for the Distributed LS-EM,
against errors in the knowledge of noise parameters.Comment: Submitted to IEEE transaction
A Probabilistic Approach for Human Everyday Activities Recognition using Body Motion from RGB-D Images
In this work, we propose an approach that relies on cues from depth perception from RGB-D images, where features related to human body motion (3D skeleton features) are used on multiple learning classifiers in order to recognize human activities on a benchmark dataset. A Dynamic Bayesian Mixture Model (DBMM) is designed to combine multiple classifier likelihoods into a single form, assigning weights (by an uncertainty measure) to counterbalance the likelihoods as a posterior probability. Temporal information is incorporated in the DBMM by means of prior probabilities, taking into consideration previous probabilistic inference to reinforce current-frame classification. The publicly available Cornell Activity Dataset [1] with 12 different human activities was used to evaluate the proposed approach. Reported results on testing dataset show that our approach overcomes state of the art methods in terms of precision, recall and overall accuracy. The developed work allows the use of activities classification for applications where the human behaviour recognition is important, such as human-robot interaction, assisted living for elderly care, among others
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