186 research outputs found
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
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