Facets for Art Gallery Problems

The Art Gallery Problem (AGP) asks for placing a minimum number of stationary guards in a polygonal region P, such that all points in P are guarded. The problem is known to be NP-hard, and its inherent continuous structure (with both the set of points that need to be guarded and the set of points that can be used for guarding being uncountably infinite) makes it difficult to apply a straightforward formulation as an Integer Linear Program. We use an iterative primal-dual relaxation approach for solving AGP instances to optimality. At each stage, a pair of LP relaxations for a finite candidate subset of primal covering and dual packing constraints and variables is considered; these correspond to possible guard positions and points that are to be guarded. Particularly useful are cutting planes for eliminating fractional solutions. We identify two classes of facets, based on Edge Cover and Set Cover (SC) inequalities. Solving the separation problem for the latter is NP-complete, but exploiting the underlying geometric structure, we show that large subclasses of fractional SC solutions cannot occur for the AGP. This allows us to separate the relevant subset of facets in polynomial time. We also characterize all facets for finite AGP relaxations with coefficients in {0, 1, 2}. Finally, we demonstrate the practical usefulness of our approach. Our cutting plane technique yields a significant improvement in terms of speed and solution quality due to considerably reduced integrality gaps as compared to the approach by Kr\"oller et al.Comment: 29 pages, 18 figures, 1 tabl

Temporal Model Adaptation for Person Re-Identification

Person re-identification is an open and challenging problem in computer vision. Majority of the efforts have been spent either to design the best feature representation or to learn the optimal matching metric. Most approaches have neglected the problem of adapting the selected features or the learned model over time. To address such a problem, we propose a temporal model adaptation scheme with human in the loop. We first introduce a similarity-dissimilarity learning method which can be trained in an incremental fashion by means of a stochastic alternating directions methods of multipliers optimization procedure. Then, to achieve temporal adaptation with limited human effort, we exploit a graph-based approach to present the user only the most informative probe-gallery matches that should be used to update the model. Results on three datasets have shown that our approach performs on par or even better than state-of-the-art approaches while reducing the manual pairwise labeling effort by about 80%

Engineering Art Galleries

The Art Gallery Problem is one of the most well-known problems in Computational Geometry, with a rich history in the study of algorithms, complexity, and variants. Recently there has been a surge in experimental work on the problem. In this survey, we describe this work, show the chronology of developments, and compare current algorithms, including two unpublished versions, in an exhaustive experiment. Furthermore, we show what core algorithmic ingredients have led to recent successes

Truth, Beauty, Freedom, and Money: Technology-Based Art and the Dynamics of Sustainability

Proposes innovative new approaches and models for art and technology institutions, and provides details for an "Arts Lab," a unique hybrid art center and research lab

Will Fair Use Survive? Free Expression in the Age of Copyright Control

"Fair use" is a crucial exception to "intellectual property" controls - it allows users to publish, distribute, or reproduce copyrighted or trademarked material without permission, for certain purposes. But extensive research, including statistical analysis and scores of firsthand stories from artists, writers, bloggers, and others, shows that many producers of creative works are wary of claiming fair use for fear of getting sued. The result is a serious chilling effect on creative expression and democratic discussion.Several factors must be considered in deciding whether a use of copyrighted material is "fair." Four factors identified in the copyright law are: 1) the purpose and character of the new work; 2) the nature of the original work; 3) the amount and substantiality of the original work that was used; and 4) the effect of the new work on the market for the original. Examples of fair use are criticism, commentary, news reporting, scholarship, and "multiple copies for classroom use." "Will Fair Use Survive?" suggests the need for strengthening fair use so that it can be an effective tool for anyone who contributes to culture and democratic discourse. The report finds: Artists, writers, historians, and filmmakers are burdened by a "clearance culture" that ignores fair use and forces them to seek permission (which may be denied) and pay high license fees in order to use even small amounts of copyrighted or trademarked material.The 1998 Digital Millennium Copyright Act (the DMCA) is being used by copyright owners to pressure Internet service providers to take down material from their servers on the mere assertion that it is infringing, with no legal judgment and no consideration of fair use.An analysis of 320 letters on the Chilling Effects website, an online repository of threatening cease and desist and "take down" letters, showed that nearly 50% of the letters had the potential to stifle protected speech. Report Highlights:The giant Bank of America sent a threatening letter to a small ceramic piggy bank company called Piggy Bank of America, claiming its use of the name was a trademark violation.A "planetary enlightenment" group called Avatar consistently suppressed online discussion group postings critical of its program by using DMCA "take down" letters.MassMutual sent a cease and desist letter to the gripe site "MassMutualSuks.com," claiming trademark infringement.Mattel sued artist Tom Forsythe for his series of "Food Chain Barbies," acerbic commentaries on Mattel's role in perpetuating gender inequality. Only after a long, bruising court fight did Forsythe win the right to parody Barbie.The report recommends: creating a clearinghouse for information, including sample replies to cease and desist and "take down" letters; outreach to Internet service providers who are instructed by companies to take down sites with material they claim as copyright-protected; changes in the law to reduce the penalty for guessing wrong about fair use; and the creation of a national pro bono legal support network.On December 15, 2005, Representatives Rick Boucher, Zoe Lofgren, and John Doolittle circulated a "Dear Colleague" letter praising the report for explaining why fair use "is a crucial part of our copyright law," and why legislation is needed to secure fair use rights in the digital environment

Cavity optomagnonics with magnetic textures: coupling a magnetic vortex to light

Optomagnonic systems, where light couples coherently to collective excitations in magnetically ordered solids, are currently of high interest due to their potential for quantum information processing platforms at the nanoscale. Efforts so far, both at the experimental and theoretical level, have focused on systems with a homogeneous magnetic background. A unique feature in optomagnonics is however the possibility of coupling light to spin excitations on top of magnetic textures. We propose a cavity-optomagnonic system with a non homogeneous magnetic ground state, namely a vortex in a magnetic microdisk. In particular we study the coupling between optical whispering gallery modes to magnon modes localized at the vortex. We show that the optomagnonic coupling has a rich spatial structure and that it can be tuned by an externally applied magnetic field. Our results predict cooperativities at maximum photon density of the order of $\mathcal{C}\approx10^{-2}$ by proper engineering of these structures.Comment: 16 pages, 11 figures, published versio