Democratic Representations

Minimization of the $\ell_{\infty}$ (or maximum) norm subject to a constraint that imposes consistency to an underdetermined system of linear equations finds use in a large number of practical applications, including vector quantization, approximate nearest neighbor search, peak-to-average power ratio (or "crest factor") reduction in communication systems, and peak force minimization in robotics and control. This paper analyzes the fundamental properties of signal representations obtained by solving such a convex optimization problem. We develop bounds on the maximum magnitude of such representations using the uncertainty principle (UP) introduced by Lyubarskii and Vershynin, and study the efficacy of $\ell_{\infty}$-norm-based dynamic range reduction. Our analysis shows that matrices satisfying the UP, such as randomly subsampled Fourier or i.i.d. Gaussian matrices, enable the computation of what we call democratic representations, whose entries all have small and similar magnitude, as well as low dynamic range. To compute democratic representations at low computational complexity, we present two new, efficient convex optimization algorithms. We finally demonstrate the efficacy of democratic representations for dynamic range reduction in a DVB-T2-based broadcast system.Comment: Submitted to a Journa

Conflicted Commons: A Local Makerspace in the Neoliberal City

The commodification of culture, space, and resources is incentivized by neoliberal urbanism. In response, we have seen an attempt to develop collectively organized, oppositional spaces within urban places. The tensions that arise when considering the production of commons in the development of the neoliberal city are the central focus of this paper. As I will observe, these spaces are subjected to commodification as they become increasingly de-politicized through neoliberal ideologies. In order to theorize about these contradictory elements, I observe a makerspace in Richmond, Virginia called HackRVA. Specifically, I consider HackRVA as an urban commons. Through in-depth interviews and participant observation, I consider how HackRVA engages with the neoliberal city of Richmond and how the organization and maintenance of their space and their community reflects commoning as social reproduction. I find that HackRVA’s relationship to the city is complicated as the community within the space both contests and assimilates to the creative economy

Initiation and spread of escape waves within animal groups

The exceptional reactivity of animal collectives to predatory attacks is thought to be due to rapid, but local, transfer of information between group members. These groups turn together in unison and produce escape waves. However, it is not clear how escape waves are created from local interactions, nor is it understood how these patterns are shaped by natural selection. By startling schools of fish with a simulated attack in an experimental arena, we demonstrate that changes in the direction and speed by a small percentage of individuals that detect the danger initiate an escape wave. This escape wave consists of a densely packed band of individuals that causes other school members to change direction. In the majority of cases this wave passes through the entire group. We use a simulation model to demonstrate that this mechanism can, through local interactions alone, produce arbitrarily large escape waves. In the model, when we set the group density to that seen in real fish schools, we find that the risk to the members at the edge of the group is roughly equal to the risk of those within the group. Our experiments and modelling results provide a plausible explanation for how escape waves propagate in Nature without centralised control

Tales of Two Referendums: Comparing Debate Quality between the UK and New Zealand Voting System Referendums of 2011

Two voting system referendums in the same year in two countries with institutional and cultural similarities provide an excellent opportunity for comparison, particularly given the significant differences in how those referendums were regulated and conducted. In New Zealand, a well-funded and balanced official information campaign led the debate; in Britain, the debate was dominated by campaign organisations. Based on content analysis of newspaper coverage of the campaigns, this paper explores how regulatory differences between these two cases shaped the quality of debate as reflected in media discourse. It finds that they made a difference, suggesting that positive interventions to promote better debate can work. It also concludes, however, that contextual factors are crucial too: interventions that work in one context will not necessarily work in another