Complex Langevin Dynamics for chiral Random Matrix Theory

We apply complex Langevin dynamics to chiral random matrix theory at nonzero chemical potential. At large quark mass the simulations agree with the analytical results while incorrect convergence is found for small quark masses. The region of quark masses for which the complex Langevin dynamics converges incorrectly is identified as the region where the fermion determinant frequently traces out a path surrounding the origin of the complex plane during the Langevin flow. This links the incorrect convergence to an ambiguity in the Langevin force due to the presence of the logarithm of the fermion determinant in the action.Comment: 23 pages, 10 figure

Full simulation of chiral Random Matrix Theory at non-zero chemical potential by Complex Langevin

It is demonstrated that the complex Langevin method can simulate chiral random matrix theory at non-zero chemical potential. The successful match with the analytic prediction for the chiral condensate is established through a shift of matrix integration variables and choosing a polar representation for the new matrix elements before complexification. Furthermore, we test the proposal to work with a Langevin-time dependent quark mass and find that it allows us to control the fluctuations of the phase of the fermion determinant throughout the Langevin trajectory.Comment: 16 pages, 6 figure

Emergent user behavior on Twitter modelled by a stochastic differential equation

Data from the social-media site, Twitter, is used to study the fluctuations in tweet rates of brand names. The tweet rates are the result of a strongly correlated user behavior, which leads to bursty collective dynamics with a characteristic 1/f noise. Here we use the aggregated "user interest" in a brand name to model collective human dynamics by a stochastic differential equation with multiplicative noise. The model is supported by a detailed analysis of the tweet rate fluctuations and it reproduces both the exact bursty dynamics found in the data and the 1/f noise

Correlations Between Human Mobility and Social Interaction Reveal General Activity Patterns

A day in the life of a person involves a broad range of activities which are common across many people. Going beyond diurnal cycles, a central question is: to what extent do individuals act according to patterns shared across an entire population? Here we investigate the interplay between different activity types, namely communication, motion, and physical proximity by analyzing data collected from smartphones distributed among 638 individuals. We explore two central questions: Which underlying principles govern the formation of the activity patterns? Are the patterns specific to each individual or shared across the entire population? We find that statistics of the entire population allows us to successfully predict 71\% of the activity and 85\% of the inactivity involved in communication, mobility, and physical proximity. Surprisingly, individual level statistics only result in marginally better predictions, indicating that a majority of activity patterns are shared across {our sample population}. Finally, we predict short-term activity patterns using a generalized linear model, which suggests that a simple linear description might be sufficient to explain a wide range of actions, whether they be of social or of physical character

Pop, Power and Politics: Kiwi FM and the ‘Third Way’ in New Zealand

In 2005 a major multi-national media company launched a New Zealand radio network that played only New Zealand music—Kiwi FM. Within a year it was clear that the experiment had failed, with the network attracting only negligible audience ratings and unsustainable commercial revenue. It was at this point that the New Zealand government stepped in, granting the network free broadcasting spectrum and significant funding in return for the ongoing promotion of New Zealand music. How this happened provides critical insights into ‘third way’ approaches to the creative industries, and in particular, local music as a cultural, political and economic commodity. Kiwi FM raises questions about national musical cultures and how artists, governments and businesses interact in these contested spaces. This article explores Kiwi FM as it moved from being a commercial enterprise to a government partner from behind the scenes, using previously unseen documents and interviews with key players in order to interrogate the utility of ‘third way’ approaches to promoting and supporting the creative industries

Measure of Node Similarity in Multilayer Networks

The weight of links in a network is often related to the similarity of the nodes. Here, we introduce a simple tunable measure for analysing the similarity of nodes across different link weights. In particular, we use the measure to analyze homophily in a group of 659 freshman students at a large university. Our analysis is based on data obtained using smartphones equipped with custom data collection software, complemented by questionnaire-based data. The network of social contacts is represented as a weighted multilayer network constructed from different channels of telecommunication as well as data on face-to-face contacts. We find that even strongly connected individuals are not more similar with respect to basic personality traits than randomly chosen pairs of individuals. In contrast, several socio-demographics variables have a significant degree of similarity. We further observe that similarity might be present in one layer of the multilayer network and simultaneously be absent in the other layers. For a variable such as gender, our measure reveals a transition from similarity between nodes connected with links of relatively low weight to dis-similarity for the nodes connected by the strongest links. We finally analyze the overlap between layers in the network for different levels of acquaintanceships.Comment: 12 pages, 4 figure

Radio New Zealand International: Reporting the Pacific in tight times

New Zealand International (RNZI) broadcasts from New Zealand into the South Pacific and is relayed to South Pacific listeners by their various national news services. In 2006, American academic Andrew M. Clark characterised the role of RNZI as ‘providing a service for the people of the South Pacific’ that also provided ‘an important public diplomacy tool for the New Zealand government’ (Clark, 2006). A decade on, this article evaluates the ongoing use and utility of RNZI as a taxpayer-funded voice of and from New Zealand, as a service for the diverse peoples of the South Pacific and as a tool of New Zealand’s transnational diplomatic efforts.  RNZI is still a key source of local and regional information and connection for the distinct cultures and nations of the vast South Pacific area, whose peoples have strong links to New Zealand through historical ties and contemporary diasporas living in the country. But, RNZI now faces mounting financial pressure, a government swinging between indifferent and hostile to public broadcasting and questions of legitimacy and reach in the ‘digital age’. With RNZI under pressure in 2016, key questions arise about its present and future. What is RNZI doing well and not so well? What role should New Zealand’s domestic and international politics play in the organisation and its outputs? And how might its importance and impact be measured and understood in such a culturally and geographically diverse region as the South Pacific? Using a variety of sources, including documents released to the author under the New Zealand Official Information Act, this article explores the role of RNZI in the contemporary New Zealand and South Pacific media environments

Complex Langevin simulations of a finite density matrix model for QCD

We study a random matrix model for QCD at finite density via complex Langevin dynamics. This model has a phase transition to a phase with nonzero baryon density. We study the convergence of the algorithm as a function of the quark mass and the chemical potential and focus on two main observables: the baryon density and the chiral condensate. For simulations close to the chiral limit, the algorithm has wrong convergence properties when the quark mass is in the spectral domain of the Dirac operator. A possible solution of this problem is discussed.Comment: 10 pages, 9 figures; Contribution to the "12th Quark Confinement and the Hadron Spectrum" conference, Thessaloniki, 28.08.-04.09.201