4,567 research outputs found
Signed Networks in Social Media
Relations between users on social media sites often reflect a mixture of
positive (friendly) and negative (antagonistic) interactions. In contrast to
the bulk of research on social networks that has focused almost exclusively on
positive interpretations of links between people, we study how the interplay
between positive and negative relationships affects the structure of on-line
social networks. We connect our analyses to theories of signed networks from
social psychology. We find that the classical theory of structural balance
tends to capture certain common patterns of interaction, but that it is also at
odds with some of the fundamental phenomena we observe --- particularly related
to the evolving, directed nature of these on-line networks. We then develop an
alternate theory of status that better explains the observed edge signs and
provides insights into the underlying social mechanisms. Our work provides one
of the first large-scale evaluations of theories of signed networks using
on-line datasets, as well as providing a perspective for reasoning about social
media sites
Governance in Social Media: A case study of the Wikipedia promotion process
Social media sites are often guided by a core group of committed users
engaged in various forms of governance. A crucial aspect of this type of
governance is deliberation, in which such a group reaches decisions on issues
of importance to the site. Despite its crucial --- though subtle --- role in
how a number of prominent social media sites function, there has been
relatively little investigation of the deliberative aspects of social media
governance. Here we explore this issue, investigating a particular deliberative
process that is extensive, public, and recorded: the promotion of Wikipedia
admins, which is determined by elections that engage committed members of the
Wikipedia community. We find that the group decision-making at the heart of
this process exhibits several fundamental forms of relative assessment. First
we observe that the chance that a voter will support a candidate is strongly
dependent on the relationship between characteristics of the voter and the
candidate. Second we investigate how both individual voter decisions and
overall election outcomes can be based on models that take into account the
sequential, public nature of the voting
Coordination and Efficiency in Decentralized Collaboration
Environments for decentralized on-line collaboration are now widespread on
the Web, underpinning open-source efforts, knowledge creation sites including
Wikipedia, and other experiments in joint production. When a distributed group
works together in such a setting, the mechanisms they use for coordination can
play an important role in the effectiveness of the group's performance.
Here we consider the trade-offs inherent in coordination in these on-line
settings, balancing the benefits to collaboration with the cost in effort that
could be spent in other ways. We consider two diverse domains that each contain
a wide range of collaborations taking place simultaneously -- Wikipedia and
GitHub -- allowing us to study how coordination varies across different
projects. We analyze trade-offs in coordination along two main dimensions,
finding similar effects in both our domains of study: first we show that, in
aggregate, high-status projects on these sites manage the coordination
trade-off at a different level than typical projects; and second, we show that
projects use a different balance of coordination when they are "crowded," with
relatively small size but many participants. We also develop a stylized
theoretical model for the cost-benefit trade-off inherent in coordination and
show that it qualitatively matches the trade-offs we observe between
crowdedness and coordination.Comment: 10 pages, 6 figures, ICWSM 2015, in Proc. 9th International AAAI
Conference on Weblogs and Social Medi
Two types of S phase precipitates in Al-Cu-Mg alloys
Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) have been used to study S phase precipitation in an Al-4.2Cu-1.5Mg-0.6Mn-0.5Si (AA2024) and an Al-4.2Cu-1.5Mg-0.6Mn-0.08Si (AA2324) (wt-%) alloy. In DSC experiments on as solution treated samples two distinct exothermic peaks are observed in the range 250 to 350°C, whereas only one peak is observed in solution treated and subsequently stretched or cold worked samples. Samples heated to 270°C and 400°C at a rate of 10°C/min in the DSC have been studied by TEM. The selected area diffraction patterns show that S phase precipitates with the classic orientation relationship form during the lower temperature peak, and for the solution treated samples, the higher temperature peak is caused by the formation of a second type of S phase precipitates which have an orientation relationship that is rotated by ~4 degrees to the classic one. The effects of Si and cold work on the formation of second type of S precipitates have been discussed
Functional connectivity during a social emotion task in adolescents and in adults
In this fMRI study we investigated functional connectivity between components of the mentalising system during a social emotion task, using psychophysiological interaction (PPI) analysis. Ten adults (22–32 years) and 18 adolescents (11–18 years) were scanned while thinking about scenarios in which a social or a basic emotion would be experienced. Unlike basic emotions (such as disgust and fear), social emotions (such as embarrassment and guilt) require the representation of another's mental states. In both adults and adolescents, an anterior rostral region of medial prefrontal cortex (arMPFC) involved in mentalising showed greater connectivity with the posterior superior temporal sulcus (pSTS) bordering on the temporo-parietal junction (TPJ) and with anterior temporal cortex (ATC) during social than during basic emotion. This result provides novel evidence that components of the mentalising system interact functionally during a social emotion task. Furthermore, functional connectivity differed between adolescence and adulthood. The adolescent group showed stronger connectivity between arMPFC and pSTS/TPJ during social relative to basic emotion than did the adult group, suggestive of developmental changes in functional integration within the mentalising system
Neutrophil Reverse Migration Becomes Transparent with Zebrafish
The precise control of neutrophil-mediated inflammation is critical for both host defense and the prevention of immunopathology. In vivo imaging studies in zebrafish, and more recently in mice, have made the novel observation that neutrophils leave a site of inflammation through a process called neutrophil reverse migration. The application of advanced imaging techniques to the genetically tractable, optically transparent zebrafish larvae was critical for these advances. Still, the mechanisms underlying neutrophil reverse migration and its effects on the resolution or priming of immune responses remain unclear. Here, we review the current knowledge of neutrophil reverse migration, its potential roles in host immunity, and the live imaging tools that make zebrafish a valuable model for increasing our knowledge of neutrophil behavior in vivo
Integrating Color, Texture, and Geometry for Image Retrieval
This paper examines the problem of image retrieval from large, heterogeneous image databases. We present a technique that fulfills several needs identified by surveying recent research in the field. This technique fairly integrates a diverse and expandable set of image properties (for example, color, texture, and location) in a retrieval framework, and allows end-users substantial control over their use. We propose a novel set of evaluation methods in addition to applying established tests for image retrieval; our technique proves competitive with state-of-the-art methods in these tests and does better on certain tasks. Furthermore, it improves on many standard image retrieval algorithms by supporting queries based on subsections of images. For certain queries this capability significantly increases the relevance of the images retrieved, and further expands the user’s control over the retrieval process
Filopodial Calcium Transients Regulate Growth Cone Motility and Guidance through Local Activation of Calpain
AbstractSpontaneous intracellular calcium ([Ca2+]i) transients in growth cone filopodia reduce filopodial motility, slow neurite outgrowth, and promote turning when generated asymmetrically; however, the downstream effectors of these Ca2+-dependent behaviors are unknown. We report that Ca2+ transients in filopodia activate the intracellular protease calpain, which slows neurite outgrowth and promotes repulsive growth cone turning upon local activation. Active calpain alters the balance between tyrosine kinase and phosphatase activities in filopodia, resulting in a net decrease in tyrosine phosphorylation, which mediates both filopodial stabilization and reduced lamellipodial protrusion. Our findings indicate that locally generated Ca2+ signals repel axon outgrowth through calpain-dependent regulation of phosphotyrosine signaling at integrin-mediated adhesion sites
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