Braid groups and Kleinian singularities

We establish faithfulness of braid group actions generated by twists along an ADE configuration of $2$-spherical objects in a derived category. Our major tool is the Garside structure on braid groups of type ADE. This faithfulness result provides the missing ingredient in Bridgeland's description of a space of stability conditions associated to a Kleinian singularity.Comment: Section 4 from versions 1 and 2 has been deleted due to an error in the proof of Theorem 2. Renamed the paper and rewrote the other sections to reflect this chang

Seeing Behind the Camera: Identifying the Authorship of a Photograph

We introduce the novel problem of identifying the photographer behind a photograph. To explore the feasibility of current computer vision techniques to address this problem, we created a new dataset of over 180,000 images taken by 41 well-known photographers. Using this dataset, we examined the effectiveness of a variety of features (low and high-level, including CNN features) at identifying the photographer. We also trained a new deep convolutional neural network for this task. Our results show that high-level features greatly outperform low-level features. We provide qualitative results using these learned models that give insight into our method's ability to distinguish between photographers, and allow us to draw interesting conclusions about what specific photographers shoot. We also demonstrate two applications of our method.Comment: Dataset downloadable at http://www.cs.pitt.edu/~chris/photographer To Appear in CVPR 201

Gaming capital: Rethinking literacy

This paper is part of the symposium: Gameplay, gameplayers and gaming capital: Exploring intersections between games, education and adolescent subjectivities in virtual worlds PEER REFEREEING REQUIRED In rethinking literacy education in light of unprecedented technological change, this paper reports on adolescent gamers and their accumulation of gaming capital. This is in opposition to more pervasive assumptions about gaming as mindless entertainment, learning simulations, ideological tools and interactive mediums for the masses. We see the need to research the medium of games in their entirety, exploring their uniqueness as a medium--while at the same time--making connections to a wider media ecology (Fuller, 2005) that includes more than the games themselves. This media ecology of videogames is demonstrated in part by the 'paratextual' (Consalvo, 2007) industries that support game play, production and design. The 'paratext' is central to gaming capital in creating individual and group systems of distinction within gaming culture. Because we understand videogames as actions across social fields enacted through the actions of players or 'operators' on software, we also deem it necessary to understand both the operator and machines' diegetic and non-diegetic actions (Galloway, 2006). This distinction allows us to think about games as more than texts, literacy practices and narratives, which highlights games' significance in technoclture as systems (Salen, 2008), procedures (Bogost, 2007), algorithms (Galloway, 2006; Wark, 2007), configurations and code (Lessig, 1999; Manovich, 2001). In conclusion we provide a series of interview questions developed to uncover adolescents' gaming capital. We also propose a heuristic to map a players' total volume of gaming capital to better understand how gaming capital establishes trajectories of exchange between cultural and economic capitals and its implications for literacy education

Another dimension from LiDAR – Obtaining foliage density from full waveform data

LiDAR tells the user where surfaces are, not what they are. In this study we investigate the potential for waveform LiDAR to provide more information on the nature of the returns over forestry. Waveform LiDAR was acquired for ten Pinus radiata plots in a New Zealand plantation, along with comprehensive leaf area sampling in 2m vertical bands. The decay rate of each waveform peak was shown to be a useful tool for estimating foliage density, and has potential for identifying regions containing ground and understorey. Leaf Area Density (LAD) is an expression of foliage density per unit height, and a relationship between waveform decay rate and LAD was developed with an R2 of 56%. Incorporating the proportion of discrete LiDAR that fell in that band (which itself has an R2 of 50%) improves this model to explain 69% of the variation in LAD. This is a good result, especially given the costs and difficulties in measuring leaf area directly. As foliage density varies dramatically on a fine scale it was not possible to differentiate the nature of every single LiDAR return – but by averaging over a small area local variation in LAD could be easily mapped. Ground returns could be distinguished as having short decays, and broad leafed understorey typically had values between those of the canopy and ground, although surface roughness and slope make it impossible to robustly identify single returns. This study produced a useful model for estimating LAD in Pinus radiata which could easily be extended to other coniferous species