3,194 research outputs found
Online Popularity and Topical Interests through the Lens of Instagram
Online socio-technical systems can be studied as proxy of the real world to
investigate human behavior and social interactions at scale. Here we focus on
Instagram, a media-sharing online platform whose popularity has been rising up
to gathering hundred millions users. Instagram exhibits a mixture of features
including social structure, social tagging and media sharing. The network of
social interactions among users models various dynamics including
follower/followee relations and users' communication by means of
posts/comments. Users can upload and tag media such as photos and pictures, and
they can "like" and comment each piece of information on the platform. In this
work we investigate three major aspects on our Instagram dataset: (i) the
structural characteristics of its network of heterogeneous interactions, to
unveil the emergence of self organization and topically-induced community
structure; (ii) the dynamics of content production and consumption, to
understand how global trends and popular users emerge; (iii) the behavior of
users labeling media with tags, to determine how they devote their attention
and to explore the variety of their topical interests. Our analysis provides
clues to understand human behavior dynamics on socio-technical systems,
specifically users and content popularity, the mechanisms of users'
interactions in online environments and how collective trends emerge from
individuals' topical interests.Comment: 11 pages, 11 figures, Proceedings of ACM Hypertext 201
Simvastatin preserves myocardial perfusion and coronary microvascular permeability in experimental hypercholesterolemia independent of lipid lowering
AbstractObjectivesThis study was designed to assess the lipid-independent effects of simvastatin on myocardial perfusion (MP) and coronary microvascular permeability index (PI) at baseline and during episodes of increased cardiac demand in experimental hypercholesterolemia.BackgroundSimvastatin preserves coronary endothelial function in experimental hypercholesterolemia independent of its lipid-lowering effect. However, the functional significance of this observation is unknown.MethodsPigs were randomized to three groups: normal diet (N), high-cholesterol diet (HC) and HC diet plus simvastatin (HC+S) for 12 weeks. Subsequently, cardiac electron beam computed tomography was performed before and during intravenous infusion of adenosine and dobutamine, and MP and PI were calculated.ResultsTotal and low density lipoprotein cholesterol levels were similarly and significantly increased in HC and HC+S animals compared with N. Basal MP was similar in all groups. Myocardial perfusion significantly increased in response to either adenosine or dobutamine in N and HC+S animals. Dobutamine also significantly increased MP in HC animals. However, the changes of MP in response to either drug were significantly lower in the HC group compared with the other two groups (p < 0.01 for adenosine and p < 0.05 for dobutamine vs. N and HC+S). Basal PI was similar in all groups and was not altered by either drug in N and HC+S animals. In contrast, PI significantly increased in HC pigs during infusion of either adenosine (p < 0.001) or dobutamine (p < 0.05).ConclusionsThese findings demonstrate that chronic administration of simvastatin preserves myocardial perfusion response and coronary microvascular integrity during cardiac stress in experimental hypercholesterolemia independent of lipid lowering
Who, if Anyone, Reacts to Accrual Information?
We confirm and extend prior research that suggests accrual levels predict future returns, even after controlling for earnings surprise. We then document abnormal buying behavior around 10-K/Q filing dates that correlates with accrual level. Specifically, we extend Collins and Hribar (2000) by showing that the accrual anomaly persists for a sample of firms followed by analysts after controlling for analyst earnings forecast errors and using exact 10-K/Q filing dates. We then show that large traders, those who
initiate trades of at least 5,000 shares, tend to trade in the correct direction in response to accrual information released in SEC filings after preliminary earnings. This tendency is limited, however, to cases
where earnings conveyed favorable news initially. Investors who use accrual information apparently ignore stocks whose earnings convey unfavorable news or believe that accrual level is not informative for
these firms. We also provide some evidence that the smallest traders react to accrual information, but in the wrong direction
A Parameterized Centrality Metric for Network Analysis
A variety of metrics have been proposed to measure the relative importance of
nodes in a network. One of these, alpha-centrality [Bonacich, 2001], measures
the number of attenuated paths that exist between nodes. We introduce a
normalized version of this metric and use it to study network structure,
specifically, to rank nodes and find community structure of the network.
Specifically, we extend the modularity-maximization method [Newman and Girvan,
2004] for community detection to use this metric as the measure of node
connectivity. Normalized alpha-centrality is a powerful tool for network
analysis, since it contains a tunable parameter that sets the length scale of
interactions. By studying how rankings and discovered communities change when
this parameter is varied allows us to identify locally and globally important
nodes and structures. We apply the proposed method to several benchmark
networks and show that it leads to better insight into network structure than
alternative methods.Comment: 11 pages, submitted to Physical Review
The Lie-Poisson structure of the reduced n-body problem
The classical n-body problem in d-dimensional space is invariant under the
Galilean symmetry group. We reduce by this symmetry group using the method of
polynomial invariants. As a result we obtain a reduced system with a
Lie-Poisson structure which is isomorphic to sp(2n-2), independently of d. The
reduction preserves the natural form of the Hamiltonian as a sum of kinetic
energy that depends on velocities only and a potential that depends on
positions only. Hence we proceed to construct a Poisson integrator for the
reduced n-body problem using a splitting method.Comment: 26 pages, 2 figure
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