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

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

Adolescent brain maturation and cortical folding: evidence for reductions in gyrification

Evidence from anatomical and functional imaging studies have highlighted major modifications of cortical circuits during adolescence. These include reductions of gray matter (GM), increases in the myelination of cortico-cortical connections and changes in the architecture of large-scale cortical networks. It is currently unclear, however, how the ongoing developmental processes impact upon the folding of the cerebral cortex and how changes in gyrification relate to maturation of GM/WM-volume, thickness and surface area. In the current study, we acquired high-resolution (3 Tesla) magnetic resonance imaging (MRI) data from 79 healthy subjects (34 males and 45 females) between the ages of 12 and 23 years and performed whole brain analysis of cortical folding patterns with the gyrification index (GI). In addition to GI-values, we obtained estimates of cortical thickness, surface area, GM and white matter (WM) volume which permitted correlations with changes in gyrification. Our data show pronounced and widespread reductions in GI-values during adolescence in several cortical regions which include precentral, temporal and frontal areas. Decreases in gyrification overlap only partially with changes in the thickness, volume and surface of GM and were characterized overall by a linear developmental trajectory. Our data suggest that the observed reductions in GI-values represent an additional, important modification of the cerebral cortex during late brain maturation which may be related to cognitive development

Three-Dimensional Recognition of Solid Objects from a Two-Dimensional Image

This thesis addresses the problem of recognizing solid objects in the three-dimensional world, using two-dimensional shape information extracted from a single image. Objects can be partly occluded and can occur in cluttered scenes. A model based approach is taken, where stored models are matched to an image. The matching problem is separated into two stages, which employ different representations of objects. The first stage uses the smallest possible number of local features to find transformations from a model to an image. This minimizes the amount of search required in recognition. The second stage uses the entire edge contour of an object to verify each transformation. This reduces the chance of finding false matches

Exploiting Sequential Phonetic Constraints in Recognizing Spoken Words

Machine recognition of spoken language requires developing more robust recognition algorithms. The current paper extends the work of Shipman and Zue by investigating the power of partial phonetic descriptions. First we demonstrate that sequences of manner of articulation classes are more reliable and provide more constraint than other classes. Alone these are of limited utility, due to the high degree of variability in natural speech. This variability is not uniform, however, as most modifications and deletions occur in unstressed syllables. The stressed syllables provide substantially more constraint. This indicates that recognition algorithms can be made more robust by exploiting the manner of articulation information in stressed syllables

Principles and Practices of Software Development

In this paper, we aim to provide a new perspective on the methods of software development. We find most software development methodologies to be overly prescriptive; they focus primarily on what methods to use without adequate consideration of what problems are being addressed and without a comparison of different methods that apply to the same problem. We maintain that software developers can be most effective if they are provided both with a variety of methods from which to choose and with the understanding necessary to select the methods that are best suited to their project. To that end, we introduce a framework for describing the principles of software development, a vocabulary for characterizing and understanding the constraints under which software is being written. We present some principles of software development, relating them to specific problems that occur in software projects and to practices that are used to address those problems. We observe that the practices of different methodologies can be understood in terms of how they weigh the relative importance of the underlying principles. We illustrate how identifying such principles can help in selecting the most appropriate practices. We note that some of the most significant differences among methodologies arise when principles provide conflicting viewpoints. We then discuss how iterative or incremental software development practices can be used to minimize the risks that result from conflicting principles. DRAFT of August 26, 2002 2

A Bayesian Framework for Model Based Tracking

We present a Bayesian framework for tracking an object in a sequence of image frames. A maximum a posteriori (MAP) recognition method is used to detect the object in each image frame, and a Kalman filter is used to estimate the true location from these observed locations. There is a natural feedback loop between the recognition method and the Kalman filter. The recognition method requires a prior on object location which is provided by the Kalman filter, and the Kalman filter requires an observed location which is provided by the recognition method. This framework has two desirable properties. First, the threshold for recognition in each frame depends on the system noise of the Kalman filter. This allows the system to identify partially occluded or distorted objects as long as the predicted locations are accurate. But requires a very good match if there is uncertainty as to the object location. Second, the search area for the recognition method is adaptively pruned using the current level of noise in the system, yielding an efficient overall method. Promising experimental results are demonstrated